µPD75212A
5.4 WATCH TIMER
The µPD75212A incorporates one channel of watch timer. The watch timer has the following functions.
• Sets the test flag (IRQW) at 0.5-second intervals.
The standby mode can be released by IRQW.
• 0.5-second interval can be set with the main system clock and subsystem clock.
• The fast mode enables to set 128-time (3.91 ms) interval useful to program debugging and inspection.
• The fixed frequencies (2.048 kHz) can be output to the P23/BUZ pin for use to generate buzzer sound and trim
the system clock oscillator frequency.
• Since the frequency divider can be cleared, the watch can be started from zero second.
Fig. 5-3 Watch Timer Block Diagram
From
Clock
Generator
fXX
128
(32.768 kHz)
fXT
(32.768 kHz)
fW
27
(256 Hz : 3.91 ms)
Selector fW
(32.768 kHz)
Frequency Divider
fW (2.048 kHz) Clear
16
fW
Selector
214
2Hz
0.5 sec
INTW
IRQW
Set Signal
Output Buffer
P23/BUZ
WM
WM7 WM6 WM5 WM4 WM3WM2 WM1 WM0
8
PORT2.3
P23
Output
Latch
Bit 2 of PMGB
Port 2
Input/Output
Mode
Internal Bus
Remarks Values at fXX = 4.194304 MHz and fXT = 32.768 kHz are indicated in parentheses.
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