PD17012_15 Datasheet, PDF (127/320 Pages) Renesas Technology Corp – 4-BIT SINGLE-CHIP MICROCONTROLLERS WITH DIGITAL TUNING SYSTEM HARDWARE

µPD17012, 17P012
Figure 12-9. Timing Chart
5V
VDD
0V
H
CE
L
BTM0CY flag setting _H
pulse (10 Hz)
L
1
BTM0CY flag
0
Program processing
AC
B
BB
B
B
BBB
A
BB
Program instruction
<1> <3> <3> <3> <3>
<3> <3> <3> <3>
<1> <3> <3>
Power-on reset
Start from address 0
Watch UP
Application of
supply voltage
BTM0CY flag detected
Point A
Watch UP
Watch UP CE reset
Start from address 0
Watch UP
Updates watch timer because
setting of BTM0CY flag (to 1)
is detected
Point B
Point C Point D
Point E
As shown in Figure 12-9, the program is started from address 0000H because the internal 10-Hz pulse
rises when supply voltage VDD is first applied.
When the BTM0CY flag is detected at point A, it is judged that the BTM0CY flag is reset (to 0) and that
a power failure (power-on reset) has occurred because the power has just been applied.
Therefore, “processing C” is executed, and the BTM0CY flag setting pulse is set to 100 ms.
Because the content of the BTM0CY flag is read once at point A, the BTM0CY flag will be set to 1 every
100 ms.
Next, even if the CE pin goes low at point B and high at point C, the program counts up the watch timer
while executing “processing B”, unless the clock stop instruction is executed.
At point C, because the CE pin goes high from low, CE reset is effected at point D at which the BTM0CY
flag setting pulse rises next time, and the program is started from address 0000H.
When the BTM0CY flag is detected at point E at this time, it is set to 1. Therefore, this is judged to be
a back up (CE reset).
As is evident from the above figure, unless the watch is updated by 100 ms at point E, the watch is delayed
by 100 ms each time CE reset is effected.
If processing A takes longer than 100 ms when a power failure is detected at point E, the setting of the
BTM0CY flag is overlooked two times. Therefore, processing A must be completed within 100 ms.
The above description also applies when the BTM0CY flag setting pulse is set to 250, 5, or 1 ms.
Therefore, the BTM0CY flag must be detected for power failure detection within the BTM0CY flag setting
time after the program has been started from address 0000H.
Data Sheet U10101EJ4V0DS
125