PD17012_15 Datasheet, PDF (282/320 Pages) Renesas Technology Corp – 4-BIT SINGLE-CHIP MICROCONTROLLERS WITH DIGITAL TUNING SYSTEM HARDWARE

µPD17012, 17P012
22.5.4 Notes on raising supply voltage VDD
When raising supply voltage VDD, keep in mind the following points (1) and (2).
(1) When raising supply voltage VDD from power-on clear voltage
It is necessary to raise supply voltage VDD to higher than 3.5 V at least once.
This is illustrated in Figure 22-7.
Suppose, for example, only a voltage less than 3.5 V is applied on application of VDD with a program that
backs up VDD at 2.3 V by using the clock stop instruction, as shown in Figure 22-7, the power-on-clear
signal is continuously output, and the program does not operate.
Because the output ports of the device output undefined values, the current consumption increases in
some cases.
If the device is backed up by batteries, therefore, the back-up time is substantially shortened.
Figure 22-7. Notes on Raising VDD
5V
3.5 V
VDD _{2.3 V}
0V
H
CE
L
H
XOUT
L
Basic timer 0 carry ^H
FF setting pulse _L
Power-on- ^H
clear signal _L
Power-on-
clear voltage
Operation stops
Current consumption may increase
during this period because
output ports are undefined.
Opera-
tion
stops
Halt status
50 ms
Normal operation
Initialization is
executed during
this period, and
then clock stop
instruction is
executed.
Back up
Power-on reset
Program starts
STOP s
instruction
280
Data Sheet U10101EJ4V0DS