UPD17073 NEC, UPD17073 Datasheet - Page 89

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

V
CE
Internal pulse
BTM0CY flag
setting pulse
BTM0CY flag
Program processing
Program instruction
DD
8 Hz
As shown in Figure 12-5, the program is started from address 0000H in synchronization with the rising of the
internal 8-Hz pulse when supply voltage V
When the BTM0CY flag is detected next at point A, the BTM0CY flag is cleared to 0 because power has been
just applied. It is therefore judged that a power failure (i.e., power-ON reset) has been detected, and
“processing C” is executed.
Because the content of the BTM0CY flag has been read once at point A, the BTM0CY flag is set to 1 every
125 ms afterward.
Next, even if the CE pin goes low at point B and goes high at point C, the program executes “processing B”
and increments the watch, unless the clock stop instruction is executed.
Because the CE pin goes high at point C, CE reset is effected at point D where the BTM0CY flag setting pulse
rises, and the program is started from address 0000H.
At this time, if the BTM0CY flag is detected at point E, it is judged that back up (CE reset) has been effected,
because the BTM0CY flag is set to 1.
As is evident from the above figure, the watch is delayed by 125 ms each time CE reset is effected, unless
the watch is updated 125 ms at point E.
If processing A takes 125 ms or longer when a power failure is detected at point E, setting of the BTM0CY
flag is overlooked two times; therefore, processing A must be completed within 125 ms.
Therefore, the BTM0CY flag must be detected for a power failure detection within the BTM0CY flag setting
time after the program has been started from the address 0000H.
Power application
3 V
0 V
H
H
H
L
L
L
1
0
Power-ON reset starts
from address 0.
A
<1>
BTM0CY flag detection
C
<3>
Point A
Figure 12-5. Timing Chart
B
Watch UP
<3>
DD
B
<3>
is applied first.
B
Watch UP
<3>
B
<3>
B
<3>
Point B
B
Watch UP
<3> <3>
B
Point C
B
Watch UP
<3><3>
CE reset starts
from address 0.
B
PD17072,17073
Point D
B
BTM0CY flag is detected.
Time updated because
flag is set to 1.
A
Point E
<1>
B
<3>
Watch UP
B
<3>
B
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