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Chapter 11
Basic I/O Interface
Introduction
µ : is great at solving problems
but if can’t communicate with outside, it is of little worth
outline some of basic methods of communications :
both serial & parallel, between humans or machines and µ
1. introduce basic I/O interface, discuss decoding for I/O
devices
2. provide detail on parallel and serial interfacing, both of
which have a variety of applications
3. connect analog-to-digital and digital-to-analog
converters, as well as both DC and stepper motors to µ
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11-1 Introduction to I/O interface
explain :
1. operation of I/O instruction(IN,INS,OUT,OUTS)
2. concept of isolated(direct or I/O mapped I/O) and
memory-mapped I/O
3. basic input and output interface
4. handshaking
I/O instructions : Table 11-1
IN,OUT : transfer data between I/O device and µ’s
accumulator(AL,AX,EAX)
variable address : 16-bit I/O address in DX
fixed address:8-bit form(p8) immediately following opcode
I/O address : port, port no, port address
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Table 11-1
Table 11-1
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11-1 Introduction to I/O interface
1st 256 I/O port address(00H~FFH) : accessed by fixed,
variable I/O instruction
0100H~FFFFH : only accessed by variable I/O address
INS : memory address is located by ES:DI
OUTS : memory address is located by DS:SI
Isolated I/O and Memory-Mapped I/O
two different methods of interfacing I/O to µ :
Isolated I/O :
most common I/O transfer technique in Intel µ based system
I/O locations : isolated from memory system
IN, INS, OUT, OUTS transfer data between µ’s
accumulator or memory and I/O
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Isolated I/O and Memory-Mapped I/O
Fig.11-1 : both isolated & memory-mapped I/O address space
PC : used for controlling peripheral devices
8-bit port address : used to access devices located on system
board
16-bit port address : used to access serial & parallel port as
well as video & disk drive systems
advantage : fully utilized memory
disadvantage :
data transferred between I/O and µ : must accessed by IN,
INS, OUT, OUTS
separate control signals : I/O read(IORC’) using M/IO’,RD’,
I/O write(IOWC’) using M/IO’, WR’
Ch.11 Basic I/O Interface
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Fig. 11-1
Fig. 11-1
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Isolated I/O and Memory-Mapped I/O
Memory-Mapped I/O
memory-mapped I/O device : treated as a memory location
in the memory map
not used IN, INS, OUT, OUTS
used any instructions that transfer data between µ & memory
advantage :
to access I/O devices : used any memory transfer instruction
disadvantage :
a portion of memory : used as I/O map
reduced circuit required for decoding : IORC’, IOWC’ have
no function
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Personal Computer I/O Map
Fig. 11-2 : I/O map for PC
0000H ~ 03FFH : reserved for computer system and
ISA bus
0400H ~ FFFFH : for user applications, main-board
functions, and PCI bus
00F8H~00FFH : for communications to coprocessor
Basic Input Interface : Fig. 11-3
3-state buffers : used to construct 8-bit input port
µ : read contents of 8 switches that connect to any 8-bit
section of data bus when select signal SEL’ = 0
when µ execute IN : I/O port address is decoded to
generate the logic 0 on SEL’
Ch.11 Basic I/O Interface
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Fig. 11-2
Fig. 11-2
Ch.11 Basic I/O Interface
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Fig. 11-3
Fig. 11-3
Ch.11 Basic I/O Interface
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Basic Output Interface
Basic Output Interface : Fig. 11-4
data latches : used to construct 8-bit output port
basic output interface : received data from µ and must
usually hold it for some external device
when OUT execute : data from accumulator are
transferred to latch via data bus
Hand Shaking :
many I/O : accept or release at a much slower rate than µ
another method of I/O control : handshaking(polling)
synchronize I/O device with µ
parallel printer : print 100 characters per second(CPS)
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Fig. 11-4
Fig. 11-4
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Handshaking
Fig. 11-5 : typical input and output of printer
D7~D0 : data connection
BUSY : indicate that printer is busy
STB’ : a clock pulse used to send data into printer
handshaking(polling)
µ poll and test BUSY pin. if busy, µ wait
if not busy, ASCII data is placed on D7~D0, and pulse is
applied to STB’ connection
printer received data, placed a logic 1 on BUSY pin
Ex. 11-1 : simple procedure that
test printer BUSY flag & send data to printer if not busy
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Fig. 11-5
Fig. 11-5
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Fig. 11-5
Fig. 11-5
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Ex. 11-1
Ex. 11-1
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Notes About Interfacing Circuitry
Input Devices
TTL level : logic 0(0.0V~0.8V) logic 1(2.0V~5.0V)
switch-based device : not TTL-compatible
Fig. 11-6 : toggle switch that is properly connected to
function as an input device
pull-up resister : usually anywhere 1K~10K ohm
used to ensure that output signal logic 1(open),
connect to ground, producing a valid logic 0(close)
Fig. 11-7 : to prevent problem with bounce(closed)
asynchronous Flip-Flop
(a) classical textbook bounce eliminator(more money)
(b) more practical version(no pull-up resister, 2 inverter)
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Fig. 11-6
Fig. 11-6
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Output Devices
Output Devices
must understand what voltages and currents are from µ
or TTL interface component
voltages : TTL-compatible from µ
logic 0 = 0.0 ~ 0.4V, logic 1 = 2.4V ~ 5.0V
currents for µ and many µ-interfacing components :
less than for standard TTL components
logic 0 = 0.0 ~ 2.0mA, logic 1 = 0.0 ~ 400 µ
Fig. 11-8 : interface a simple LED to a µ peripheral pin
(a) : a transistor driver (b) TTL inverter
LED : required 10mA of forward bias current to light
assume : voltage drop=2.0V(nominal 1.65V, 1.5~2.0V)
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TTL compatible(74LS..)
input voltage : 0(~0.8V), 1(2V~)
input current : 0( ~ -0.2mA : 0.4V), 1(~ 20A : 2.7V)
output voltage : 0(~0.4V : 12mA), 1(2.4V : -2mA~)
output current : 0(~24mA), 1(~ -15mA)
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Output Devices
current-limit resister = 3V/10ma = 300Ω ≒ 330Ω
∵ 300Ω : not a standard resistor values
(a) 2N2222 : general-purpose switching TR(gain=100)
base current=collector current/gain=10mA/100=0.1mA
TTL input signal = minimum 2.4V
voltage drop across emitter-base junction = 0.7V
base current-limiting resistor=1.7V/0.1mA=17K≒18K
12V DC motor : current = 1A
not used TTL inverter : two reason
1. 12V : burn out the inverter
2. exceed 16mA maximum current from inverter
2N2222 TR : maximum current 250mA~500mA
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Fig. 11-9
Darlington-pair : Fig. 11-9
minimum current gain=7000, maximum current=4A
1A/7000 = 0.143mA, (2.4-1.5)V/0.143=6.29K≒6.2K
Darlington-pair : heat-sink
diode : used to prevent Darlington-pair from being
destroyed by inductive kick-back from motor
this circuit : also used to interface mechanical relays
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11-2 I/O Port Address Decoding
similar to memory address decoding, especially
for memory-mapped I/O
main difference : between memory decoding & isolated
I/O decoding
no of address pins connected to the decoder
memory(A31~, A23~, A19~A0), isolated I/O(A15~A0)
used only fixed I/O addressing : decode only A7~A0
another difference : use IORC’, IOWC’(M/IO’,RD’,WR’)
Decoding 8-bit I/O addresses
fixed I/O instruction : used 8-bit I/O port address that
appear on A15~A0 as 0000H~00FFH
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11-2 I/O Port Address Decoding
Fig. 11-10 : decode 8-bit I/O ports F0H~FFH
Fig. 11-11 : using PAL for decoder(74AS138)
Ex. 11-2 : PAL program
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Fig. 11-11
Fig. 11-11
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Decoding 16-bit I/O Addressing
Fig. 11-12 : used PAL 16L8, 8-input NAND
NAND gate output : A15~A8(EF00H~EFFFH)
PAL 16L8 : A7~A0(EFF8H~EFFFH)
Ex. 11-3 : program for PAL 16L8
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Ex. 11-3
Ex. 11-3
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8- and 16-bit I/O Ports
I/O system : 8-bit I/O banks, just as memory
Fig. 11-13 : separate I/O banks for 16-bit system
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8- and 16-bit I/O Ports
separate write strobe: any 8-bit I/O write of two I/O banks
note : all I/O ports use 8-bit addresses
Fig. 11-14 : two different 8-bit output devices located at
8-bit I/O address 40H, 41H(Ex. 11-4 : PAL program)
port 40H,41H : addressed as separate 8-bit ports, or
together as one 16-bit port
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Fig. 11-14
Fig. 11-14
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8- and 16-bit I/O Ports
Fig. 11-15 : 16-bit input device connected to function at
8-bit I/O addresses 64H, 65H
Ex. 11-5 : enable signal of 3-state buffers(74LS244)
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Fig. 11-15
Fig. 11-15
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32-bit Wide I/O Ports
32-bit wide I/O port : not common
eventually become commonplace because newer buses
EISA system bus, VESA local, current PCI bus
Fig.11-16:32-bit input port for 32-bit µ(8-bit port 70~73H)
Ex. 11-6 : PAL program
/SEL=/IORC*/A7*A6*A5*A4*/A3*/A2=0111 00xx
64-bit Pentium µ :
8-bit I/O port 0034H : Pentium I/O bank 5
16-bit I/O port 0034H~0035H : I/O bank 5,6
32-bit I/O port 0100H~0103H : I/O bank 0~3
widest I/O transfer : 32 bits, no 64-bit I/O instructions
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Fig. 11-16
Fig. 11-16
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11-3 The Programmable Peripheral Interface
82C55 PPI : programmable peripheral interface
very popular, low-cost interfacing component
24 pins for I/O : programmable in groups of 12 pins
groups that operate in three distinct modes of operation
interface any TTL-compatible I/O device to µ
require wait states if operated with µ higher than 8MHz
provided at least 2.5 mA of sink current at each output,
with a maximum of 4.0 mA
Fig. 11-17 : pin-out diagram
three I/O ports A,B,C : programmed as groups
group A : port A(PA7~PA0), PC7~PC4 of port C
group B : port B(PB7~PB0), PC3~PC0 of port C
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Fig. 11-17
Fig. 11-17
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11-3 The Programmable Peripheral Interface
A1~A0 : select an internal register for programming or
operation(Table 11-2)
PC system : 82C55 is decoded at I/O ports 60H~63H
for keyboard control, for controlling speaker, timer
Fig. 11-18 : 82C55 connected to 80386SX
8-bit I/O port addresses C0H(port A), C2H(port B),
C4H(port C), C6H(command register)
interfaced low bank of 80386SX I/O map
RESET : initialized 82C55 whenever µ is reset
all ports : set up as simple input ports using mode 0
internally programmed input pins after RESET
damage: prevented when power is 1st applied to system
Ch.11 Basic I/O Interface
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Table 11-2
Table 11-2
Ch.11 Basic I/O Interface
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Fig. 11-18
Fig. 11-18
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Fig. 11-19
Fig. 11-19
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Programming the 82C55
82C55 : programmed through two internal command reg.
bit 7 of command byte : 1(command byte A), 0(“ B)
command byte A : programmed function of group A, B
command byte B : set or reset bits of port C only if
82C55 is programmed in mode 1 or 2 : Fig.11-19
group B(port B, PC3~PC0) : operated in either mode 0, 1
mode 0 : basic input/output mode
group B : programmed as buffered input, latched output
mode 1 : strobed operation
data : transferred through port B
handshaking signal : provided by port C
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Programming the 82C55
group A(port A, PC7~PC4):operated in either mode 0,1,2
mode 2 : operated bi-directional mode for port A
Mode 0 Operation
function either as buffered input or latched output
Fig. 11-20 : connected to eight 7-segment LED display
port A, B : programmed as latched output port(mode 0)
port A : provided segment data output to display
port B : provided a means of selecting one display
position at a time for multiplexing display
I/O port no.s : 0700H~0703H
Ex. 11-7 : program for PAL 16L8
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Ex. 11-7
Ex. 11-7
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Fig. 11-20
Fig. 11-20
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Mode 0 Operation
resister values :
average current 10mA per segment
segment current = 80mA(8ea10mA)
segment load resister : (5 - 0.2 - 1.65 - 0.2)V/80mA 
3.0V/80mA = 36.875Ω  39Ω
minimum gain of transistor : 100
base current of segment switch : 80mA/100 = 0.8mA
logic 1 output voltage of 82C55 : typical 3.0 V
base resister : (3 – 0.7)V/0.8mA = 2.875KΩ  2.2KΩ
base current of anode switch : 70mA/100 = 0.7mA
base resister : (5 – 0.7 – 0.4)V/0.7mA = 5.57KΩ
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Mode 0 Operation
Ex. 11-8 : programmed port A, B as outputs
Ex. 11-9: procedure to multiplex the
displays(MSD=right)
procedure DELAY : cause a 1 ms time delay
recommended display flash : 100 ~ 1500 Hz
light each digit : 1 ms
total display flash rate : 1000 Hz/8 display = 125 Hz
eight 7-segment code : stored at MEM ~
MEM+7(MSD)
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Ex. 11-9
Ex. 11-9
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An LCD Display Interfaced to the 82C55
LCD(liquid crystal display) : quickly replacing LED
disadvantage : difficult to see in low-light situations
Fig. 11-21 : Optrex DMC-20481(4 line  20 ch.) LCD
accept ASCII code as input data
also accept command to initialize, control its application
data connections : attached to 82C55 port A
used to input display data
and to output information from display
four control pins : VEE, RS, E, R/W’
VEE : to adjust the contrast of LCD
normally connected to 10K potentiometer
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Fig. 11-21
Fig. 11-21
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An LCD Display Interfaced to the 82C55
RS(resister select) :
data(RS=1) or instructions(RS=0)
E(enable) : logic 1 to read or write information
R/W’ : select a read or a write operation
two inputs for back-lighting LED, which not shown
normally, RS(1 or 0), R/W’(1 or 0), data input pins(data)
and then E pin is pulsed to access the LCD
initialization : accomplished via following steps
1. wait at least 15ms after Vcc rise to 5.0V
2. output function set command(30H), wait at least 4.1ms
3. output function set command(30H) a second time, wait
at least 100 ㎲
Ch.11 Basic I/O Interface
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An LCD Display Interfaced to the 82C55
4. output function set command(30H) a third time, wait
at least 40 ㎲
5. output function set command(38H) a fourth time,
wait at least 40 ㎲
6. output a 08H to disable display, wait at least 40 ㎲
7. output a 01H to home cursor and clear display, wait
at least 1.64 ms
8. output the enable display cursor off(0CH), wait at
least 40 ㎲
9. output a 06H to select auto-increment, shift cursor,
wait at least 40 ㎲
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An LCD Display Interfaced to the 82C55
Ex. 11-10 : initialization
three time delays : DELAY15, DELAY41, DELAY100
clock tick : used for all timing
NOP(in OUTCMD procedure) : to ensure that E bit
remain a logic 1 long enough to activate LCD display
Table 11-3 : command used in initialization dialog
to display information and control the display :
needed a few procedure
no longer needed time delay : test busy flag bit
Ex. 11-11 : BUSY procedure
test LCD and only return when display has completely
a prior instruction
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Ex. 11-10
Ex. 11-10
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Ex. 11-10
Ex. 11-10
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Table 11-3
Table 11-3
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Ex. 11-11
Ex. 11-11
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An LCD Display Interfaced to the 82C55
Ex. 11-12 : WRITE procedure
used BUSY to test before trying to write new data to
display
transfer ASCII character from BL to current cursor
position of display
initialization : cursor for auto-increment
Ex. 11-13 : CLS procedure
clear and home cursor : at least 1.64 ms time delay
used DELAY41 instead of a call to BUSY
inside display RAM : 128 bytes(00H~7FH)
2 line  40 ch : 1st(00H~27H), 2nd(40H~67H)
4  20 ch : 1st(00H~), 2nd(40H~), 3rd(14H~), 4th(54H~)
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Ex. 11-12
Ex. 11-12
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Ex. 11-13
Ex. 11-13
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A Stepper Motor Interfaced to the 82C55
stepper motor : digital motor because
it is moved in discrete steps as it traverse through 360°
geared to move 15°(common)~1° per step(high-precision)
steps: gained through many magnetic poles and/or gearing
Fig. 11-22 : four-coil step motor that use an armature with a
single pole(energized two coils : 45°,135°,225°,315°)
Fig. 11-23 : stepper motor interfaced to 82C55
driven by using NPN Darlington amplifier pairs to
provide a large current to each coil
Ex. 11-14 : procedure(port A : programmed in mode 0)
CX : hold no of steps and direction of rotation
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Fig. 11-22
Fig. 11-22
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Fig. 11-23
Fig. 11-23
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Ex. 11-14
Ex. 11-14
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A Stepper Motor Interfaced to the 82C55
CX > 8000H : spin in right-hand direction
CX < 8000H : spin in left-hand direction
remaining 15-bit(removed LSB of CX) : no of steps
1 ms time delay(not illustrated) : required to allow
stepper-motor armature time to move to its next position
current position : stored in memory location POS
33H, 66H, 0CCH, 99H : ROR(step right), ROL(step
left)
full step :
eight step sequence : 11H,33H,22H,66H,44H,0CCH,88H,99H
0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°
half step mode : energized one coil(0°, 90°, 180°, 270°)
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Key Matrix Interface
keyboard : vast variety of sizes
from standard 101-key to small specialized "(4-16 keys)
Fig. 11-24 : small key-matrix
16 switches(44) interfaced to port A, B of 82C55
4 rows(Row0~3 : PA0~3), 4 col.(Col0~Col3 : PB0~3)
each row : connected to 5.0V through 10K pull-up reg.
to ensure that row is pulled high when no push-button
switch is closed
decoded at I/O ports 50H~53H by PAL(no program)
port A : programmed as input port to read the rows
port B : programmed as output port to select a column
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Fig. 11-24
Fig. 11-24
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Key Matrix Interface
port B pins PB3-PB0 = 1110 : Col0 = logic 0
selected four keys in column 0
switch 0-3 = closed : one of PA3-PA0 = logic 0
switch 4-F = closed : port A = remained logic 1
Fig. 11-25 : flowchart
to read a key from keyboard
and debounce the key(short time delay of 10-20ms)
1. wait for release of a key
2. wait for a keystroke
3. calculated position of the key
Ex. 11-15 : main keyboard procedure(KEY)
SCAN:to scan keys, DELAY:waste 10ms for debouncing
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Fig. 11-25
Fig. 11-25
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Ex. 11-15
Ex. 11-15
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Ex. 11-15
Ex. 11-15
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Mode 1 Strobed Input
Mode 1 : Fig. 11-26
port A and/or port B to function as latching input devices
port C : used for control or handshaking signal
signal definition for mode 1 strobed input :
STB’(strobe) input :
capture external data into port latch on 0-to-1 transition
activate IBF(input buffer full), INTR(interrupt request)
port latch : hold data until µ read it via IN instruction
µ : notice through software(IBF) or hardware(INTR)
IBF output : indicated that input latch contain information
INTR output : requested an interrupt
=1:when STB’ return to 1, =0:when µ read data via IN
Ch.11 Basic I/O Interface
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Fig. 11-26
Fig. 11-26
73
Mode 1 Strobed Input
INTE(interrupt enable) signal : neither input nor output
internal bit programmed via PC4(port A), PC2(port B)
PC7, PC6 : available for any general-purpose I/O
keyboard : excellent example of strobed input device
debounced a key-switches
provided strobed signal whenever a key is depressed
data output contained the ASCII-coded key code
Fig. 11-27 : keyboard connected to strobed input port A
DAV’(data available) : connected to STB’
activated for 1.0µs each time that a key is typed
each time a key is typed : data is stored into port A
Ex. 11-16 : procedure
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Fig. 11-27
Fig. 11-27
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Ex. 11-16
Ex. 11-16
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Mode 1 Strobed Output
Fig. 11-28 :
signal definition for mode 1 strobed output :
OBF’(output buffer full) output :
0: whenever data are output(OUT) to port A, B latch
1: whenever ACK’ pulse return from external device
ACK’(acknowledge) input : indicate that
external device has received the data from 82C55 port
INTR output : often requested an interrupt
when external devices receive data via ACK’
qualified by internal INTE’ bit
INTE’ : neither input nor output
internal programmed bit via PC6(port A), PC2(port B)
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Fig. 11-28
Fig. 11-28
78
Mode 1 Strobed Output
PC5, PC4 : general-purpose I/O pins
printer interface(Fig.11-29) : strobed output
example
port B : connected to parallel printer
PC2 : ACK’ to acknowledge the receipt of ASCII ch.
DS’(data strobe) to strobe data into printer
PC4 : used with software that generate DS’ signal
Ex. 11-17 : software that send ASCII-coded character in
AH to printer
1. test OBF’, if not wait
if OBF’=1 : send AH to printer through port B and also
send DS’ signal
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Fig. 11-29
Fig. 11-29
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Ex. 11-17
Ex. 11-17
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Mode 2 Bi-directional Operation
port A only : bi-directional
mode 1 strobed input and output
useful when interfacing two computers
used for IEEE-488 parallel high-speed GPIB(general
purpose instrumentation bus) interface standard
Fig. 11-30 :
the bi-directional bus
used by referencing port A with IN, OUT instructions
Ex. 11-18 : to transmit data through bi-directional bus
Ex. 11-19 : to receive data through bi-directional bus
INTR : activated from both directions of data flow
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Fig. 11-30
Fig. 11-30
83
Ex. 11-18
Ex. 11-18
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Ex. 11-19
Ex. 11-19
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82C55 Mode Summary
Fig. 11-31 : graphical summary of three mode
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11-4 8279 programmable keyboard/display interface
scan and encode up to a 64-key keyboard and
control up to a 16-digit numerical display
keyboard interface :
built-in FIFO buffer that allow to store up to 8
keystrokes before µ must retrieve a character
display interface :
internal 168 RAM that store coded display information
Basic Description of the 8279 : Fig. 11-32
A0 input : select data or control for read and write
A0=0 : data, A0=1 : control or status register
BD’(blank) output : used to blank the display
Ch.11 Basic I/O Interface
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Fig. 11-32
Fig. 11-32
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8279
CLK : generate internal timing
max. 3.125MHz : 8279-5, 2.0MHz : 8279
CN/ST(control/strobe) input : normally connected to Control
key on a keyboard
DB7-DB0(data bus) : bi-directional pins
IRQ(interrupt request) output : 1 whenever a key is pressed
indicate that keyboard data are available for µ
OUTA3-OUTA0 : send data to display(most-significant)
OUTB3-OUTB0 : send data to display(least-significant)
CS’, RD’, WR’, RESET, Vcc(+5.0V), Vss(ground)
RL7-RL0(return line) input : used to sense any key depression
SHIFT input : normally connected to Shift key on a keyboard
SL3-Sl0(scan line) output : scan both keyboard and display
Ch.11 Basic I/O Interface
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Interfacing 8279 to Microprocessor
Fig. 11-33 : 8279 connected to 8088(8 MHz)
decoded at 8-bit I/O address 10H(data), 11H(control
port)
Ex. 11-20 : PAL 16L8 program
WAIT2’ : used to cause two wait states
Fig. 11-34 : keyboard interface
keyboard matrix : any size from 22 to 88 matrix
key : normal open push-button switch
74LS138 : generate eight low column strobe signal
SL2-Sl0 : sequentially scan each column of keyboard
8279 : scan RL pins(internal pull-up resister)
8 control word : Table 11-4
Ch.11 Basic I/O Interface
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Fig. 11-33
Fig. 11-33
Ch.11 Basic I/O Interface
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Ex. 11-20
Ex. 11-20
Ch.11 Basic I/O Interface
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Fig. 11-34
Fig. 11-34
Ch.11 Basic I/O Interface
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Table 11-4
Table 11-4
Ch.11 Basic I/O Interface
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8279 Control Word
000 DD MMM : mode set
DD : select mode of operation for display(Table 11-5)
select 8- or 16-digit display
determine whether new data are entered to rightmost
or leftmost display position
MMM : select mode of operation for keyboard(T. 11-6)
encoded mode : SL output = active high, and follow
binary bit pattern 0 through 7, or 0 through 15,
depending whether 8- or 16-digit displays are
selected
decoded mode : SL output repeat pattern
1110,1101,1011,0111
strobed mode : active high pulse on CN/ST input pin
strobe data from RL into internal FIFO
Ch.11 Basic I/O Interface
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Table 11-5
Table 11-5
Ch.11 Basic I/O Interface
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8279 Control Word
2-key lock-out : prevent two keys from being
recognized if pressed simultaneously
N-key rollover : accept all keys pressed simultaneously,
from 1st to last
001 PPPPP : clock command
programmed internal clock divider
PPPPP : prescaler that divide clock input pin(CLK) to
achieve the desired operating frequency of
approximately 100KHz
CLK=1MHz : PPPPP=1010=010102, CLK=3MHz : 30=111102
010 Z 0 AAA : read FIFO
select address of a keystroke from internal FIFO buffer
AAA : select desired FIFO location from 000 to 111
Ch.11 Basic I/O Interface
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8279 Control Word
Z : auto-increment for address
011 Z AAAA : display read
select read address of one of display RAM position
AAAA : address of position to be read
Z : auto-increment for address
100 Z AAAA : write display
select write address of one of display
A… : address position to be written to through data port
101 0 WW BB : display write inhibit
inhibit writing to either half of each display RAM location
left W : inhibit writing to leftmost 4 bits
BB : blank(turn off) either half of output pins
Ch.11 Basic I/O Interface
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8279 Control Word
110 0 CCFA : clear
clear display, FIFO, or both display and FIFO(All)
F : clear FIFO and display RAM status, set address
pointer to 000
CC = 00 or 01 : all of display RAM ⇒ 00H(0000 0000)
CC = 10 : 20H(space, 0010 0000)
CC = 11 : FFH(1111 1111)
111 E 000 : end of interrupt
to clear IRQ pin to zero in sensor matrix mode
E=1 : used special error mode
status reg. indicate if multiple key closure have occur
Ch.11 Basic I/O Interface
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8279
initialization of keyboard interface(Fig.11-34) :
1. determined clock divider: 3MHz/30(111102)=100KHz
2. program keyboard type : encoded, 2-key lockout
3. program operation of FIFO
Ex. 11-21
Ch.11 Basic I/O Interface
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8279
Ex. 11-22 : procedure to read data from keyboard
FIFO status register : Fig. 11-35
NNN=000 : FIFO empty
FIFO not empty : inputs data to AL, return
101
Fig. 11-35
Fig. 11-35
Ch.11 Basic I/O Interface
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Fig. 11-36
Fig. 11-36 : format of scanned and strobed mode
scanned code : converted to ASCII by using XLAT
instruction with ASCII code lookup table
returned with CT, SH and row, column no.
SH, CT : show state of shift pin, control pin
strobed mode : 8 RL inputs appear as they are sampled
by placing a logic 1 on strobe input pin to 8279
Ch.11 Basic I/O Interface
103
Six-Digit Display Interface
Fig. 11-37 : interfaced 6-digit numeric display to 8088
PAL 16L8 : decoded 8279 at I/O port 20H, 21H
segment data : supplied displays through OUTA,OUTB
buffered by segment driver(ULN2003A)
3-to-8 decoder(74ALS138) : enable anode switch
(5-0.2-1.65-0.4)/60mA=2.75/0.06=45.847Ω
(5-0.7-0.4)/80mA/100=3.9/0.8mA=4.875K=4.8K
Ex. 11-23 : initialization
Ex. 11-24 : procedure for displaying
data : transferred to procedure through AX
AH : 7-segment display code
AL : address of displayed digit
Ch.11 Basic I/O Interface
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Fig. 11-37
Fig. 11-37
105
Ex. 11-23,24
Ex. 11-23,24
106
11-5 8254 Programmable Interval Timer
8254: 3 independent 16-bit programmable counters(timers)
each counter : capable of counting in binary or BCD
maximum allowable input frequency : 10MHz
useful to control real-time events
ex of usage : real-time clock, event counter, motor
speed and direction control
PC : decoded at ports 40H~43H(8253 instead of 8254)
1. generate a basic timer interrupt(≈18.2Hz): clock tick
2. cause DRAM memory to be refreshed(15µs)
3. provide timing source to internal speaker and other
devices
Ch.11 Basic I/O Interface
107
8254
Fig. 11-38 : pin-out and internal block diagram
each timer : CLK input, gate input, OUT output
CLK : provide basic operating frequency to the timer
often connected to PCLK from µ system bus controller
gate pin : control timer in some modes
always sampled on rising edge of CLK
OUT pin : obtain the output of timer
A1, A0 : select one of four internal reg.(Table 11-7)
00,01,10,11 : counter 0,1,2, control word
programming the 8254
each counter : individually programmed by control word
Fig. 11-39 : control word
Ch.11 Basic I/O Interface
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Fig. 11-38
Fig. 11-38
Ch.11 Basic I/O Interface
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Table 11-7
Table 11-7
Ch.11 Basic I/O Interface
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Fig. 11-39
Fig. 11-39
Ch.11 Basic I/O Interface
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8254
each counter : programmed with a count of 1 to FFFFH
count of 0 : equal to FFFFH + 1(65536) or 10000(BCD)
all modes of operation : minimum count of 1
except modes 2, 3(minimum count of 2)
timer 0 in PC : divide by count of 64K to generate
18.2Hz(18.196Hz) interrupt clock tick
(4.77MHz/4=1.1925MHz)/65536 = 18.196Hz
programmed two bytes into counter :
1st byte(LSB) : will stop the count
2nd byte(MSB) : start counter with new count
Ex. 11-25 : show two method to program counter 1,2
Ch.11 Basic I/O Interface
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Ex. 11-25
Ex. 11-25
Ch.11 Basic I/O Interface
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Modes of operation
Fig. 11-40 : functions six modes with CLK, gate, OUT
mode 0 : interrupt on terminal count
typically used for event counting
OUT = 0 : when control word is written and until
counter reach zero
G : no effected on OUT, =1:enable counting, =0:disable
mode 1 : hardware retriggerable one-shot
monostable multivibrator : one-shot pulse
G : trigger, retrigger counter
mode 2 : rate generator
functions like a divide-by-N counter
Ch.11 Basic I/O Interface
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Fig. 11-40
Fig. 11-40
115
Fig. mode 0
Fig. mode 0
116
Fig. mode 1
Fig. mode 1
117
Fig. mode 2
Fig. mode 2
118
Modes of operation
generate a series of continuous pulses(one clock pulse
width)
count = 10 : OUT=1 for 9 clock, =0 for one clock period
cycle : repeated until programmed counter with new
count or G = 0
G = 0 to 1 : initiate new counting
mode 3 : square wave mode
generate a continuous square-wave
typically used for Baud rate generation
count=even : high for one-half, low for one-half of count
count=odd : high for one clocking period longer than low
Ch.11 Basic I/O Interface
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Fig. mode 3
Fig. mode 3
120
Modes of operation
mode 4 : software triggered strobe
produce a single pulse at OUT
count= 10 : OUT=1 for 10 clock, =0 for one clock period
OUT : initially high
G : no effected on OUT, =1:enable counting, =0:disable
cycle : not begin until counter loaded new count
mode 5 : hardware triggered strobe(retriggerable)
like as mode 4, except that started by trigger pulse on G
similar to mode 1 : retriggerable
GATE operation :
minimum, maximum initial count :
Ch.11 Basic I/O Interface
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Fig. mode 4
Fig. mode 4
122
Fig. mode 5
Fig. mode 5
123
Fig. GATE operation
Fig. GATE operation
Ch.11 Basic I/O Interface
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Fig. min, max initial count
Fig. min, max initial count
Ch.11 Basic I/O Interface
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Generating a Wave-form with 8254
Fig. 11-41 : 8254 connected to 80386SX
I/O port : 0700H, 0702H, 0704H, 0706H
address : decoded by using a PAL 16L8
Ex. 11-26 :
CLK0,1 = 8MHz
OUT0 = 100KHz square-wave : mode 3 for counter 0
100KHz = 8 MHz / 80
OUT1=200KHz continuous pulse: mode 2 for counter 1
200KHz = 8MHz / 40
Ch.11 Basic I/O Interface
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Fig. 11-41
Fig. 11-41
Ch.11 Basic I/O Interface
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Ex. 11-26
Ex. 11-26
128
8254 Programmable Interval Timer
Reading a Counter
each counter : have an internal latch
latch : normally follow the count
can remember the count by programming the
counter latch control word(Fig. 11-42)
held contents of counter until it is read
read-back control word(Fig. 11-43) : read more than
one counter at same time
CNT’ = 0 : counters selected by CNT0, CNT1, CNT2
ST’ =0 : latched status register
Ch.11 Basic I/O Interface
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Fig. 11-39
Fig. 11-39
Ch.11 Basic I/O Interface
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Fig. 11-42,43
Fig. 11-42,43
Ch.11 Basic I/O Interface
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8254
status register : Fig. 11-44
Ch.11 Basic I/O Interface
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DC Motor Speed and Direction Control
Fig. 11-45 : 8254 as DC motor speed controller
JK FF’s Q = 1 : U4C, U4D inverter’s output = 0
Q3’s base = 0 ∴Q3 = saturation, Q4’s base = 0 ∴Q4 = cutoff
Q’ = 0 : U4A, U4B inverter’s output = 1
Q1’s base = 1 ∴Q3 = cutoff, Q2’s base = 1 ∴Q2 = saturation
current : +12V → Q3 → motor -, + →Q2 → ground
cause the motor to spin in its reverse direction
forward direction : Q = 0(Q’ = 1)
Q alternated between 1 and 0 : motor spin in either
direction at various speeds
duty cycle of Q = 50% : not spin at all
Fig. 11-46 : timing for motor speed and direction
Ch.11 Basic I/O Interface
133
Fig. 11-45
Fig. 11-45
134
Fig. 11-46
Fig. 11-46
135
DC Motor Speed and Direction Control
each counter : generate pulses at different position to vary
the duty cycle at Q = pulse width modulation
counter 0,1 : programmed to divide input clock by 30720
duty cycle of Q : by changing point at which counter 1 is
started in relationship to counter 0
260.42Hz = 8MHz/30720 : operating frequency
60Hz < operating frequency < 1000Hz
256(8 bit) different speed = 30720/256 = 120
Ex.11-27:procedure that control speed & direction of motor
speed : controlled by value of AH(00H~80H~FFH)
reverse direction max speed, stop, forward max speed
BX=30720-(AH*120)
start counter 1, start counter 0 when counter 1=BX
Ch.11 Basic I/O Interface
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Ex. 11-27
Ex. 11-27
Ch.11 Basic I/O Interface
137
Ex. 11-27
Ex. 11-27
Ch.11 Basic I/O Interface
138
11-6 16550 Programmable communications interface
16550 : designed to connect to any type of serial interface
universal asynchronous receiver/transmitter(UART)
capable of operating at 0 ~ 1.5 M Baud
Baud rate : no of bits transferred per second, including
start, stop, data, and parity
included programmable Baud rate generator, separate
FIFOs for input and output data
each FIFO : 16 bytes of storage
Asynchronous Serial Data : Fig. 11-47
transmitted & received without a clock or timing signal
frame : a start bit, seven data bits, parity, one stop bit
ASCII character : 10 bits
Ch.11 Basic I/O Interface
139
16550 Functional Description
Fig. 11-48 : pin-out of 16550
140
16550 Functional Description
40-pin DIP(dual in-line package) : Fig 11-48,
44 pin PLCC(plastic lead-less chip carrier)
able function in simplex, half-duplex, full-duplex mode
simplex : transmitter or receiver is used by itself such as
FM(frequency modulation) radio station
half-duplex : transmit and receive, but not both at same
time such as CB(citizens band) radio
full-duplex : allow transmit and receive in both
directions simultaneously
16550 : control a modem(modulator/demodulator)
convert TTL levels of serial data into audio tones that
can pass through telephone system
Ch.11 Basic I/O Interface
141
16550 Functional Description
six pin : devoted to modem control
DSR’(data set ready) input : indicate that modem or data
set is ready to operate
DTR’(data terminal ready) output : indicate that data
terminal(16550) is ready to function
CTS’(clear-to-send) input : indicate that modem or data
set is ready to exchange information. used in half-duplex
RTS’(request-to-send) output : indicate that UART wish
to send data
RI’(ring indicator) input : by modem to indicate that
telephone is ringing
DCD’(data carrier detect) input : used by modem to
signal the 16550 that a carrier is present
Ch.11 Basic I/O Interface
142
16550 Pin Functions
modem : data set equipment(DTE), data communication
equipment(DCE)
16550 : referred to as data terminal
A0,A1,A2(Fig.11-8) : select internal reg. and data transfer
Ch.11 Basic I/O Interface
143
16550 Pin Functions
ADS’(address strobe) input : latch address lines and
chip select lines
CS0, CS1, CS2’(chip select) : all active to enable 16550
D7~D0 : data bus
BAUDOUT’ : clock signal generated by BAUD rate
generator from transmitter section.
connected to RCLK input to generate a receive clock
RCLK(receiver clock) : clock to receiver section
always 16  desired receiver Baud rate
DDIS(disable driver) output : logic 0 to indicate that µ
is reading data from UART
can used to change direction of data flow through a buffer
INTR(interrupt request) output : to µ
Ch.11 Basic I/O Interface
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16550 Pin Functions
MR(master reset) input : initialize 16550
connected to system RESET signal. interrupt disable
RD, RD’ input(either) : cause data to be read from register
specified by address input
WR, WR’ input(either) : cause to transfer command and
data to 16550
SIN(serial input) : accept serial data
SOUT(serial output) : transmit serial data
RXRDY’(receiver ready) : used to transfer received data
via DMA
TXRDY’(transmitter ready) : used to transfer transmitter
data via DMA
XIN, XOUT : connected crystal, or external timing source
Ch.11 Basic I/O Interface
145
Programming the 16550
two part : initialization dialog, operation dialog
initialization dialog : after HW/SW reset
1. programming line control register(A2,A1,A0=011)
2. Baud rate generator(enable divisor latch : line control reg)
divisor : LSB = 000, MSB = 001 (A2,A1,A0)
3. enable FIFO(A2,A1,A0=010)
1. line control register : Fig. 11-49
select no of data bit, no of stop bit, parity
I/O port : 011(A2,A1,A0)
Table 11-9 : ST, P, PE bit
SB(send break)=1 : break is transmitted from SOUT pin
break : at least two frame of logic 0 data
Ch.11 Basic I/O Interface
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Fig. 11-49
Fig. 11-49
Ch.11 Basic I/O Interface
147
Table 11-9
Table 11-9
Ch.11 Basic I/O Interface
148
Table 11-10
2. programming Baud rate : Table 11-10
16-bit divisor :
I/O port : A2,A1,A0 = 000(LSByte), 001(MSByte)
divisor=240 : 18.432MHz/(16240)=4800 Baud
Ch.11 Basic I/O Interface
149
Programming the 16550
Fig. 11-50 : interface 16550 to 8088
using PAL 16L8 to decode F0H~F7H
Ex. 11-28 : asynchronous system required
7 data bits, odd parity, Baud rate of 9600
FIFO control register : Fig. 11-51
I/O port = 010 (Table 11.8)
line status register(I/O port=101) : Fig. 11-52
error condition, state of transmitter and receiver
Sending Serial Data : Ex. 11-29
transmit the contents of AH
polled TH bit
Ch.11 Basic I/O Interface
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Fig. 11-50
Fig. 11-50
Ch.11 Basic I/O Interface
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Ex. 11-28
Ex. 11-28
Ch.11 Basic I/O Interface
152
FIFO control register : Fig. 11-51
I/O port(A2,A1,A0) = 010 (Table 11.8)
Ch.11 Basic I/O Interface
153
line status register : Fig. 11-52
I/O port(A2,A1,A0) = 101 (Table 11.8)
error condition, state of transmitter and receiver
Ch.11 Basic I/O Interface
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Sending Serial Data : Ex. 11-29
transmit the contents of AH, polled TH bit
Ch.11 Basic I/O Interface
155
Programming the 16550
Receiving Serial Data : Ex. 11-30
test DR bit
return with AL(ASCII ‘?’) : if detected error
UART Errors : occur during normal operation
parity error : indicate the received data with wrong parity
encountered noise during reception
framing error : start, stop bits are not in proper places
received data at an incorrect Baud rate
overrun error : data have overrun the internal receiver
FIFO buffer
only if s/w fail to read data from UART before FIFO is full
BI(break indicator) bit : not checked
break : two consecutive frame of logic 0s on SIN pin of UART
Ch.11 Basic I/O Interface
156
Ex. 11-30
Ex. 11-30
Ch.11 Basic I/O Interface
157
11-7 ADC and DAC converters
used to interface µ to the analog world
DAC0830 Digital-to-Analog converter
fairly common, low cost, medium speed(≈1.0µs)
8-bit converter : transform 8-bit no into analog voltage
generate 28 bit=256 different voltage levels
Fig. 11-53 : pin-out of DAC0830
D7~D0 : 8-bit digital input(binary no)
Iout1, Iout2 : analog output
designed as input to external operational amplifier
-Vref(reference voltage) : = -5V
output step voltage(resolution) = 5/(256-1)=5/255=0.0196V
input=146=10010010 : 1465/255 = 2.862V
Ch.11 Basic I/O Interface
158
Fig. 11-53
Fig. 11-53
Ch.11 Basic I/O Interface
159
DAC0830 Digital-to-Analog converter
internal structure of DAC0830 : Fig. 11-54
two internal latch : transparent latch
1st (holding reg.) : hold byte while 2nd is converted
2nd : connect to R-2R internal ladder converter
in many case, only use 2nd latch for entering data
IDLE=1, CS’=0
transparent latch :
G=1: data pass through the latch, G=0: data are latched or held
Fig. 11-55 : DAC0830 connected to µ
PAL 16L8 : decoded I/O port 20H
OUT 20H, AL
-12V zener reference voltage : full output voltage=+12V
Ch.11 Basic I/O Interface
160
Fig. 11-54
Fig. 11-54
Ch.11 Basic I/O Interface
161
Fig. 11-55
Fig. 11-55
Ch.11 Basic I/O Interface
162
ADC0804 Analog-to-Digital Converter
common, low cost, required up to 100µs to convert
used for many applications that do not require a high
degree of accuracy
Fig. 11-56 : pin-out of ADC0804
to start conversion process : WR’=pulsed , CS=0
INTR( interrupt request) : end of conversion
required a considerable amount of time(100 µs) for conversion
Ch.11 Basic I/O Interface
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ADC0804 Analog-to-Digital Converter
timing diagram : Fig. 11-57
pulsed WR’, wait(100µs) for INTR to return to logic 0,
then read data from converter
option : connected INTR pin to interrupt input
interrupt occur : when conversion is complete
164
ADC0804 Analog-to-Digital Converter
Analog Input Signal : Fig. 11-58
VI+, VI- : connected to internal OP amp
1st way : used single input(0V~+5.0V)
2nd : applied variable voltage to VI-, so adjusted zero
reference for VI+
165
ADC0804 Analog-to-Digital Converter
Generating the Clock Signal
permissible range of clock frequency : 100~1460KHz
as close as possible to 1460KHz : minimum conversion time
1. external clock applied to CLK IN, or
2. generated with RC circuit : Fig. 11-59
Fclk = 1/(1.1RC)=1/(1.11030.00110-6)=1/1.110-6=909KHz
Ch.11 Basic I/O Interface
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ADC0804 Analog-to-Digital Converter
Connecting ADC0804 to 8086 µ : Fig. 11-60
decoded I/O port 40H for data, 42H for INTR signal
Vref : not attached to anything, which is normal
Ex. 11-31 : procedure for start and read data
polled INTR bit until logic 0
return with AL, containing converted digital code
167
Fig. 11-60
Fig. 11-60
Ch.11 Basic I/O Interface
168
Using ADC0804 and DAC0830
Fig. 11-61 : to capture and replay audio signal or speech
ADC0804 : I/O ports 0700H, 0702H
DAC0830 : I/O port 0704H
I/O ports : low bank of 16-bit µ 8086, 80386SX
Ex. 11-32 :
read a 1 second burst of speech, play it back 10 times
repeat until system is turned off
speech: sampled, stored in section of memory(WORDS)
sample rate : 2048 samples/sec
Ch.11 Basic I/O Interface
169
Fig. 11-61
Fig. 11-61
170
Ex. 11-32
Ex. 11-32
Ch.11 Basic I/O Interface
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Ex. 11-32
Ex. 11-32
Ch.11 Basic I/O Interface
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Ex. 11-32
Ex. 11-32
Ch.11 Basic I/O Interface
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