UPD75208 NEC, UPD75208 Datasheet - Page 17

• Manufacturer Part Number: UPD75208
• Description: 4-BIT SINGLE-CHIP MICROCOMPUTER
• Manufacturer: NEC

5.4
Remarks Values at f
From
Clock
Generator
The PD75208 incorporates one channel of watch timer. The watch timer has the following functions:
• Sets the test flag (IRQW) at 0.5 sec intervals.
• 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
• Since the frequency divider can be cleared, the watch can be started from zero second.
The standby mode can be released by IRQW.
and trim the system clock oscillator frequency.
WATCH TIMER
128
f
(32.768 kHz)
(32.768 kHz)
f
XT
XX
WM
WM7 WM6 WM5 WM4
XX
= 4.194304 MHz and f
Selector
(32.768 kHz)
f
W
Internal Bus
8
Fig. 5-3 Watch Timer Block Diagram
WM3
XT
f
16
W
= 32.768 kHz are indicated in parentheses.
WM2
(2.048 kHz)
Frequency Divider
WM1
Clear
WM0
2
f
W
7
(256 Hz : 3.91 ms)
P23
Output
Latch
PORT2.3
0.5 sec
f
2
W
2Hz
14
Selector
Port 2
Input/Output
Mode
Output Buffer
Bit 2 of PMGB
INTW
IRQW
Set Signal
PD75208
P23/BUZ
17