UPD75218 NEC, UPD75218 Datasheet - Page 18

• Manufacturer Part Number: UPD75218
• Description: 4-BIT SINGLE-CHIP MICROCOMPUTER
• Manufacturer: NEC

18
5.4
Remark Values when f
Caution When the main system clock operates at 6.0 MHz, a time interval of 0.5 second cannot be produced.
The PD75218 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.
From
clock
generator
The standby mode can be released by IRQW.
and trim the system clock oscillator frequency.
WATCH TIMER
Before producing this time interval, the main system clock must be changed to the subsystem clock.
128
f
(32.768 kHz)
(32.768 kHz)
XT
f
XX
WM
WM7 WM6 WM5 WM4
XX
is 4.194304 MHz and f
Selector
(32.768 kHz)
f
W
Fig. 5-3 Watch Timer Block Diagram
8
WM3
f
16
W
XT
WM2
is 32.768 kHz are indicated in parentheses.
(2.048 kHz)
Internal bus
Frequency divider
WM1
Clear
WM0
2
f
W
7
(256 Hz : 3.91 ms)
P23
output
latch
PORT2.3
0.5 sec
f
2
2 Hz
W
14
Selector
Port 2
input/output
mode
Output buffer
Bit 2 of PMGB
PD75218
INTW
IRQW
set signal
P23/BUZ