UPD17073 NEC, UPD17073 Datasheet - Page 88

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

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(3) Adjusting basic timer 0 at CE reset
An example of adjusting the basic timer 0 at CE reset is shown on the next page.
As shown in this example, the timer may have to be adjusted if the BTM0CY flag is used for power failure
detection and, at the same time, the flag is used for a watch timer.
When the power is applied the first time (power-ON reset), the BTM0CY flag is cleared to “0”, and not set until
the contents of the flag is read again by an instruction shown in Table 12-1.
If the CE pin goes high, CE reset is effected in synchronization with rising edge of the BTM0CY flag setting
pulse. At this time, the BTM0CY flag is set to “1” and starts.
Therefore, it can be judged, when system reset (power-ON reset or CE reset) has been effected, whether the
system reset is power-ON reset or CE reset, by checking the status of the BTM0CY flag.
That is, if the BTM0CY flag is “0”, power-ON reset has been effected; if the flag is “1”, CE reset has been effected
(for power failure detection).
At this time, the watch timer must continue its operation even when CE reset has been effected.
However, because the BTM0CY flag is cleared to “0” as a result of reading the BTM0CY flag to detect a power
failure, the set (1) status of the BTM0CY flag is overlooked once.
Consequently, it is necessary to update the watch timer if CE reset has been detected as a result of power
failure detection.
For details on power failure detection, refer to 20.6 Power Failure Detection.
Example Adjusting timer at CE reset (to detect power failure and update watch by BTM0CY flag)
Figure 12-5 shows the timing chart of the above program.
START:
BACKUP:
LOOP:
INITIAL:
; <2>
; <3>
; <1>
Processing A
BANK1
SKT1
BR
Updates watch 125 ms. ; Adjusts watch because this is back up (CE reset)
Processing B
SKF1
BR
BR
Processing C
BR
BTM0CY
INITIAL
BTM0CY
BACKUP
LOOP
LOOP
; Program address 0000H
; Embedded macro
; Tests BTM0CY flag.
; If BTM0CY is “0”, branches to INITIAL (power failure detection).
; While performing processing B,
; tests BTM0CY flag and updates watch.
; Initialization of ports and peripheral hardware.
PD17072,17073