µPD75304B,75306B,75308B
5.5 WATCH TIMER
The µPD75308B incorporates a single watch timer channel. The watch timer has the following functions.
• Sets test flags (IRQW) at 0.5 second intervals. The standby mode can be released with IRQW.
• 0.5 sec. time intervals can be created in either the main system clock or the subsystem clock.
• In the fast watch mode, time intervals which are 128 times normal (3.91 ms) can be set, making this
function convenient for program debugging and testing.
• A fixed frequency (2.048 kHz) can be output to the P23/BUZ pin for use in generating buzzer sounds and
trimming system clock oscillation frequencies.
• The frequency divider can be cleared, so this clock can be started at 0 second.
Fig. 5-4 Watch Timer Block Diagram
f
W
26
(512 Hz : 1.95 ms)
f
LCD
f
W
27
(256 Hz : 3.91 ms)
INTW
IRQW
Set Signal
f
W
Selector
f
W
214
128
(32.768 kHz)
From
Clock
Generator
f
W
Selector
Frequency Divider
Clear
(32.768 kHz)
2Hz
f
XT
0.5 sec
(32.768 kHz)
f
16
W
(2.048 kHz)
Output Buffer
P23/BUZ
WM
PORT2.3
Bit 2 of PMGB
P23
Port 2
Input/Output
Mode
Output
WM7
0
0
0
8
WM3 WM2
WM1
WM0
Latch
Bit Test Instruction
Internal Bus
Remarks Values in parentheses are when fX = 4.194304 MHz and fXT = 32.768 kHz.
25
NEC [ NEC ]
