Renesas R8C/15 Información técnica Pagina 95

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R8C/14 Group, R8C/15 Group 12. Watchdog Timer
Rev.2.10 Jan 19, 2006 Page 81 of 253
REJ09B0164-0210
12.1 When Count Source Protection Mode Disabled
The count source of the watchdog timer is the CPU clock when count source protection mode is
disabled. Table 12.2 lists the Specification of Watchdog Timer (When Count Source Protection Mode is
Disabled).
NOTES:
1. The watchdog timer is reset when writing “00h” to the WDTR register before writing “FFh”. The
prescaler is reset after the microcomputer is reset. Some errors occur by the prescaler for the
period of the watchdog timer.
2. The WDTON bit cannot be changed by a program. When setting the WDTON bit, write “0” to the bit
0 of the address 0FFFFh by a flash writer.
Table 12.2 Specification of Watchdog Timer (When Count Source Protection Mode is Disabled)
Item Specification
Count Source CPU clock
Count Operation Decrement
Period
Division ratio of prescaler(n) x count value of watchdog timer(32768)
(1)
CPU clock
n : 16 or 128 (selected by WDC7 bit in WDC register)
e.g.When the CPU clock is 16MHz and prescaler is divided by 16, the
period is approximately 32.8ms
Count Start Condition
The WDTON bit
(2)
in the OFS register (0FFFFh) selects the operation
of watchdog timer after reset
When the WDTON bit is set to “1” (watchdog timer is in stop state
after reset)
The watchdog timer and prescaler stop after reset and the count
starts by writing to the WDTS register
When the WDTON bit is set to “0” (watchdog timer starts
automatically after exiting )
The watchdog timer and prescaler start counting automatically after
reset
Reset Condition of Watchdog
Timer
Reset
Write “00h” to the WDTR register before writing “FFh”
Underflow
Count Stop Condition Stop and wait modes (inherit the count from the held value after exiting
modes)
Operation at the time of
Underflow
When the PM12 bit in the PM1 register is set to “0”
Watchdog timer interrupt
When the PM12 bit in the PM1 register is set to “1”
Watchdog timer reset (refer to 5.5 Watchdog Timer Reset)
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