UPD75316B datasheet(21/77 Pages) NEC

21 / 77 page

µPD75312B, 75316B

5.5

WATCH TIMER

The

µPD75316B incorporates a 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-second time intervals can be created in either the main system clock or the subsystem clock.

• In the rapid feed 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 oscillator frequencies.

• The frequency divider can be cleared, enabling creation of watches that can start from 0 second.

Fig. 5-4 Watch Timer Block Diagram

Remark

Values in parentheses are when fX = 4.194304 MHz and fXT = 32.768 kHz.

Internal Bus

WM7

WM3 WM2 WM1 WM0

Bit Test Instruction

P23

Output

Latch

Port 2

Input/Output

Mode

PORT2.3

Bit 2 of PMGB

P23/BUZ

Output Buffer

Selector

Frequency Divider

Clear

(2.048 kHz)

fLCD

(512 Hz : 1.95 ms)

(256 Hz : 3.91 ms)

(32.768 kHz)

Selector

From

Clock

Generator

128

(32.768 kHz)

fXT

(32.768 kHz)

INTW

IRQW Set

Signal

2Hz

0.5 sec

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