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RL78 POC and LVD
Renesas Electronics Corporation
© 2010 Renesas Electronics Corporation. All rights reserved.
00000-A
Introduction
 Purpose
 This course provides an introduction to the RL78 Power-On-Clear
and Low Voltage Detector.
 Objective
 Learn about the RL78 POC and LVD features and its capabilities.
 Content
 18 pages (including this page)
 Learning Time
 20 minutes
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POC Power-On-Clear
3
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Power-On-Clear Circuit
 Functions
 Generates internal reset signal at power on
 Compares supply voltage VDD and detection voltage VPOC
VDD >= 1.51V ± 0.03V and generates internal reset signal when
VDD < 1.50V ± 0.03V
 CPU can also be released by LVD, selectable by an option byte
 Current consumption already included in STOP mode current
 Block Diagram
4
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Power-On-Clear Circuit
 Operation LVD is off VPOC0 to VPOC2 = 0x07
Undefined
area
The supply voltage enters the undefined area
If this may happen in the system, the LVD must
be used in combination.
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LVD Low-Voltage-Detector
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Low-Voltage-Detector Circuit
 Functions
 Compares the supply voltage VDD with detection voltage VLVIH,
VLVIL and generates a reset or internal interrupt
 Detection voltage is selectable by option byte
– 14 levels (1.63V～4.06V)
 Three different operation modes available
– interrupt and reset mode
– Reset mode
– Interrupt mode
 Very low power consumption of only 0.1uA
 LVD is operating is STOP mode
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Block diagram of LVD
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Option byte for LVD
 Functions of this register
 Select base operation mode of the LVD
 Select voltage level of LVD
Address : 000C1H/010C1H
7
6
5
4
3
2
VPOC2
VPOC1
VPOC0
1
LVIS1
LVIS0
VPOC2-0,LVIS0,1
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1
LVIMDS1 LVIMDS0
Set detection voltage by combination
LVIMDS1
LVIMDS0
selection LVD operation mode
0
0
Setting prohibited
0
1
Interrupt mode
1
0
interrupt & Reset mode
1
1
Reset mode
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0
Low-Voltage Detector levels
 Detection voltage levels
When used as reset mode, or interrupt mode
Detection voltage (TYP.)
Detection voltage (TYP.)
14 levels
can be selected.
10
When used as interrupt & reset mode
© 2010 Renesas Electronics Corporation. All rights reserved.
LVD control register LVIM
 Functions of this register
 Write enable for LVIS
 Status flags for LVD operation
LVIM
7
6
5
4
3
2
1
0
LVISEN
0
0
0
0
0
LVIOMSK
LVIF
LVISEN
Write enable for LVIS
0
Disabling rewriting to LVIS
1
Enabling rewriting to LVIS
LVIOMSK
0
1
Mask status flag of LVD detection
LVD operation enabled
LVD operation waiting
LVIOMSK is set to 1 automatically after LVISEN =1.
After rewriting LVIS, LVD detection needs stabilization.
LVIOMSK =1 during rewriting LVIS and during stabilization.
Therefore after clear LVISEN to 0, LVIOMSK is kept 1 during stabilization time of about 200us to
300us .
LVIF
0
1
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voltage detection status flag
VLVI =< VDD
VDD =< VLVI
LVD control register LVIS
 Functions of this register
 Mode selection (LVIMD)
 Voltage level selection (LVILV)
 It is possible to write to LVIS register in interrupt & reset mode if LVISEN =1.
 In interrupt mode or reset mode it isn't possible to change the value of LVIS.
Interrupt & reset mode
Interrupt mode
Address : FFFAAH After reset : 00H / 01H / 81H
Reset mode
Symbol
7
6
5
4
3
2
1
0
LVIS
LVIMD
0
0
0
0
0
0
LVILV
12
LVIMD
0
1
Selection of LVD detection mode
Interrupt mode
Reset mode
LVILV
0
1
LVD detection voltage level
High-voltage detection level
Low-voltage detection level
© 2010 Renesas Electronics Corporation. All rights reserved.
Different LVD modes
 Different Objectives and the right LVD mode
Objective
Mode to be used
LVD should be used to
RESET mode
A substitute an external reset IC. Reset generation at the preselected voltage.
Switch device in secure
B state/standby in case of low
voltage.
Interrupt mode
Interrupt generation at the preselected voltage.
Save important data before
Interrupt (detection notice) and reset mode
reset by low voltage detection. Interrupt generation at the preselected voltage
C
and finally reset generation at reset voltage.
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Example A: external reset IC
 Supervise guaranteed voltage range of CPU
 To avoid operation outside specified area
Operation condition
frequency
Voltage
LVD setting
: HOCO 32MHz
: 5V
Option byte 00C1H :“0111 1111B”
LVD detection voltage : VLVI5 (rise 2.81V(typ.) fall 2.70(min.))
LVD mode : reset mode
LVD reset release. and
CPU start operation.
LVD
POR
2.81V(typ.)
Reset by LVD
CPU
operable
2.7V(min.)
CPU
inoperable
1.51V
->time
CPU state
14
POR reset
LVD reset
CPU operation
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LVD reset
POR reset
Example B: Switch device to standby
 Supervise guaranteed voltage range of CPU and set device into
standby to avoid operation outside specified area
Operation condition
frequency
voltage
LVD setting
Option byte 00C1H :“0011 1101B”
: HOCO 8MHz
: 3V
LVD detection voltage : VLVI11 (rise 1.88V(typ.)、fall 1.8V(min.))
LVD mode : interrupt mode
Reset release by LVD only
rising supply voltage. and
start operation CPU.
LVD
1.88V(typ.)
Cause interrupt by LVD.
then switching to
standby by software.
CPU
operable
1.80V(min.)
Reset by POR.
Stopped RTC
POR
CPU
inoperable
1.51V
->time
CPU state
POR reset
LVD reset
RTC state
POR reset
LVD reset
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CPU operation
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STOP
RTC operation
POR reset
POR reset
Example C: Save data before reset
 Supervise guaranteed voltage range of CPU and save
parameters before enter reset.
Operation condition
frequency
voltage
LVD setting
Option byte 00C1H : “0101 0110B”
: HOCO 8MHz
: 3V
LVD detection voltage Reset release voltage
Reset voltage
Interrupt voltage
: VLVI6 2.71V(typ.)
: VLVI8 2.40V(min.)
: VLVI6 2.60V(min.)
LVD mode : interrupt (detection notice)& reset mode
LVD reset release and
CPU operation start.
LVD is set to interrupt
Cause interrupt by LVD. Then
switching LVD to reset automatically.
saving important data by software.
2.71V(typ.)
2.60V(min.)
LVD
CPU
operable
Reset by LVD
2.40V(min.)
CPU
inoperable
POR
->time
CPU state
16
POR reset
LVD reset
CPU operation
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saving data
LVD reset
POR reset
Summary
 Power on Clear
 Functions
 Block Diagram
 Operation
 For more information, visit:
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 LVD





Functions
Block Diagram
Option Bytes
Registers
Operation Modes
Renesas Electronics Europe
© 2010 Renesas Electronics Corporation. All rights reserved.