UPD17073 NEC, UPD17073 Datasheet - Page 202

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UPD17073

Manufacturer Part Number
UPD17073
Description
4-BIT SINGLE-CHIP MICROCONTROLLER WITH HARDWARE FOR DIGITAL TUNING SYSTEM
Manufacturer
NEC
Datasheet

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20.6.2 Notes on power failure detection with BTM0CY flag
202
(1) Updating watch
(2) Watch updating processing time
(3) Power failure detection timing
Keep in mind the following points when using the BTM0CY flag for watch counting:
When creating a watch program by using the basic timer 0, it is necessary to update the watch after a power
failure has been detected.
This is because watch counting is skipped once because the BTM0CY flag is read when a power failure has
been detected, and thus the BTM0CY flag is cleared to 0.
To update the watch, its processing must be completed before the next basic timer 0 carry FF setting pule
rises.
This is because CE reset is effected without the watch updating processing completed if the CE pin goes high
while the watch updating processing is in progress.
For further information on (1) and (2) above, refer to 12.2.5 (3) Adjusting basic timer 0 at CE reset.
To perform power failure processing, the following points must be noted.
Watch counting with the BTM0CY flag must be completed before the next basic timer 0 carry FF setting pulse
rises after the BTM0CY flag for power failure detection has been read and the program has been started from
address 0000H.
This is because, the basic timer 0 carry FF setting time is 125 ms, and if power failure detection is performed
126 ms after the program has been started, the BTM0CY flag is not detected once.
For details, refer to 12.2.5 (3) Adjusting basic timer 0 at CE reset.
Moreover, power failure detection and initial processing must be completed within the basic timer 0 carry FF
setting time, as shown in the example on the next page.
This is because, if he CE pin rises and CE reset is effected during power failure detection or initial processing,
the processing is interrupted, resulting in troubles.
To change the basic timer 0 carry FF setting time in the initial processing, one instruction must be used to
change the setting time at the end of the initial processing.
PD17072,17073

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