UPD17015GS datasheet(48/120 Pages) NEC

48 / 120 page

µPD17015

Fig. 10-6 Timing Chart

3.0 V

0 V

VDD

8 Hz

internal pulse

BTM0CY flag

set pulse

BTM0CY flag

Program

processing

Program

instruction

Supply voltage

applied

Start at address 0

on a power-on reset

Timer

incre-

mented

Timer

incre-

mented

Timer

incremented

Timer

incremented

Timer

incremented

BTM0CY flag detected

Start at

address 0

on a CE

reset

Timer updated because

the BTM0CY flag has

been detected to be

set (1)

Point A

Point B

Point C

Point D

Point E

As shown in Fig. 10-6, when supply voltage VDD is applied, the 8 Hz internal pulse rises to make the program

start at address 0000H.

When the BTM0CY flag is detected at point A, the BTM0CY flag appears to be cleared (0) because it is just after

power is supplied. Consequently, it is determined that a power failure (power-on reset) has occurred. Then,

process C is performed.

So, process C is performed to select 100 ms as the BTM0CY flag set pulse.

Because the BTM0CY flag is once read-accessed at point A, the BTM0CY flag will be set (1) at intervals of 125

ms.

Even when the CE pin goes to a low at point B and goes to a high at point C, the program continues to update

the clock while performing process B, unless the clock stop instruction is executed.

Because the CE pin goes from a low to a high at point C, a CE reset occurs at point D, where the BTM0CY flag

set pulse rises, to start the program at address 0000H.

When the BTM0CY flag is detected at point E, it is determined that a backup (CE reset) has occurred, because

the flag appears to be set (1).

Also, as easily seen from the figure, if the clock is not updated by 125 ms at point E, the clock loses 125 ms every

time a CE reset occurs.

If process A takes more than 125 ms to detect for a power failure at point E, it is impossible to detect the BTM0CY

flag for two cycles.

Therefore, process A must be performed within 125 ms.

It is necessary, therefore, to detect the BTM0CY flag for power failure detection after the program starts at address

0000H and before the BTM0CY flag is set.

UPD17015GS Datasheet(PDF) 48 Page - NEC

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