7549 datasheet(45/86 Pages) RENESAS

45 / 86 page

Rev.2.02

Mar 31, 2009

Page 43 of 81

REJ03B0202-0202

7549 Group

Fig 55. Block diagram of watchdog timer

•Notes

(1) The watchdog timer operates in wait mode. To prevent

underflow, write to the watchdog timer control register.

The watchdog timer stops in stop mode, but starts counting

at the same time as exiting stop mode. After exiting stop

mode, it continues counting during oscillation stabilization

time. To prevent underflow during the period, the watchdog

timer H count source selection bit (bit 7) in the watchdog

timer control register (address 003916) should be set to “0”

before executing the STP instruction.

Note that the watchdog timer continues counting even if the

STP instruction is executed in the following two conditions:

1 Stopping the low-speed on-chip oscillator: Disabled (bit

4 in FSROM2)

Source clock of the watchdog timer: Low-speed on-chip

oscillator/16 (bit 0 in FSROM2)

2 Stopping the low-speed on-chip oscillator: Disabled (bit

4 in FSROM2)

Source clock of the watchdog timer:

φSOURCE (bit 0 in

FSROM2)

φSOURCE: Low-speed on-chip oscillator (bits 5 and 4 in

CLKM)

(2) STP instruction function selection bit

The function of the STP instruction can be selected by the

bit 2 in FSROM2. This bit cannot be used for rewriting by

executing the STP instruction.

• When this bit is set to “0”, stop mode is entered by

executing the STP instruction.

• When this bit is set to “1”, internal reset occurs by

executing the STP instruction.

Watchdog timer H (8)

Data bus

Watchdog timer L (8)

“FF16” is set at

WDTCON writing

1/16

φSOURCE

Low-speed on-chip

oscillator

Watchdog timer source

clock selection bit

(bit 0 of FSROM2)

Watchdog timer disable bit

(bit 1 of FSROM2)

Reset

circuit

Internal reset

STP instruction function

selection bit

(bit 3 of FSROM2)

STP Instruction

Reset pin input

Watchdog timer H

count source selection bit

(bit 7 of WDTCON)

Watchdog timer H count source

initial value selection bit

(bit 2 of FSROM2)

FSROM2: Function set ROM data 2

WDTCON: Watchdog timer control register

CPUM: CPU mode register

“FF16” is set at

WDTCON writing

Initial value setting

after releasing reset

“0”

“1”

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