M38B53M4-059FP datasheet(233/355 Pages) MITSUBISHI

233 / 355 page

38B5 Group User’s Manual

APPLICATION

2-145

2.8 Watchdog timer

2.8.3 Watchdog timer application examples

Outline: When a program runs away, the watchdog timer makes the microcomputer return to the

reset state.

Specifications: •When the watchdog timer H underflows, it is judged as incorrect program, and the

microcomputer is returned to the reset state.

•Bit 7 of the watchdog timer control register is set to “0” at 1-cycle intervals in the

main routine before underflow of the watchdog timer H. (Initialization of watchdog

timer value)

•Use of watchdog timer L underflow as count source of watchdog timer H

•Setting of main clock division ratio to f(XIN) (high-speed mode)

Figure 2.8.3 shows the connection of watchdog timer and the setting of the division ratio.

Figure 2.8.4 shows the setting of relevant registers.

Fig. 2.8.3 Connection of watchdog timer and setting of division ratio

Fig. 2.8.4 Setting of relevant registers

f(XIN) = 4 MHz

RESET

Watchdog timer L

Watchdog timer H

Internal reset

STP instruction disable bit

STP instruction

1/8

1/2561/4096

Reset

circuit

Fixed

CPU mode register (address 003B16)

CPUM

High-speed (f(XIN)) mode operation

Watchdog timer control register (address 002B16)

STP instruction: Enabled

WDTCON

Single-chip mode

Main clock (XIN-XOUT): Oscillating

Internal system clock: XIN-XOUT

Watchdog timer H count source:

Underflow of watchdog timer L

M38B53M4-059FP Datasheet(PDF) 233 Page - Mitsubishi Electric Semiconductor