M30201 datasheet(46/172 Pages) RENESAS

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Mitsubishi microcomputers

M30201 Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Watchdog Timer

Write to the watchdog timer

start register

(address 000E16)

RESET

Watchdog timer

interrupt request

Watchdog timer

Set to

“7FFF16”

1/128

1/16

“CM07 = 0”

“WDC7 = 1”

“CM07 = 0”

“WDC7 = 0”

“CM07 = 1”

BCLK

1/2

Prescaler

Figure 1.34. Block diagram of watchdog timer

Watchdog Timer

The watchdog timer has the function of detecting when the program is out of control. The watchdog timer is

a 15-bit counter which down-counts the clock derived by dividing the BCLK using the prescaler. A watchdog

timer interrupt is generated when an underflow occurs in the watchdog timer. When XIN is selected for the

BCLK, bit 7 of the watchdog timer control register (address 000F16) selects the prescaler division ratio (by

16 or by 128). When XCIN is selected as the BCLK, the prescaler is set for division by 2 regardless of bit 7

of the watchdog timer control register (address 000F16).

When XIN is selected in BCLK

Watchdog timer cycle =

When XCIN is selected in BCLK

Watchdog timer cycle =

For example, when BCLK is 10MHz and the prescaler division ratio is set to 16, the watchdog timer cycle is

approximately 52.4 ms.

The watchdog timer is initialized by writing to the watchdog timer start register (address 000E16) and when

a watchdog timer interrupt request is generated. The prescaler is initialized only when the microcomputer is

reset. After a reset is cancelled, the watchdog timer and prescaler are both stopped. The count is started by

writing to the watchdog timer start register (address 000E16). In stop mode and wait mode the watchdog

timer and prescaler are stopped. Counting is resumed from the held value when the modes are released.

Figure 1.34 shows the block diagram of the watchdog timer. Figure 1.35 shows the watchdog timer-related

registers.

Prescaler division ratio (16 or 128) x watchdog timer count (32768)

BCLK

Prescaler division ratio (2) x watchdog timer count (32768)

BCLK

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