221
Bit 2: CKS2
Bit 1: CKS1
Bit 0: CKS0
Clock Division Ratio
Overflow Period
(when P
φ
= 15 MHz)
0
0
0
1
(Initial value)
17
µ
s
1
1/4
68
µ
s
1
0
1/16
273
µ
s
1
1/32
546
µ
s
1
0
0
1/64
1.09 ms
1
1/256
4.36 ms
1
0
1/1024
17.48 ms
1
1/4096
69.91 ms
Note:
If bits CKS2–CKS0 are modified when the WDT is running, the up-count may not be
performed correctly. Ensure that these bits are modified only when the WDT is not running.
9.7.3
Notes on Register Access
The watchdog timer counter (WTCNT) and watchdog timer control/status register (WTCSR) are
more difficult to write to than other registers. The procedure for writing to these registers is given
below.
Writing to WTCNT and WTCSR: These registers must be written to using a word transfer
instruction. They cannot be written to with a byte or longword transfer instruction. When writing
to WTCNT, set the upper byte to H'5A and transfer the lower byte as the write data, as shown in
figure 9.3. When writing to WTCSR, set the upper byte to H'A5 and transfer the lower byte as the
write data. This transfer procedure writes the lower byte data to WTCNT or WTCSR.
15
8
7
0
H'5A
Write data
Address: H'FFFFFE84
WTCNT write
15
8
7
0
H'A5
Write data
Address: H'FFFFFE86
WTCSR write
Figure 9.3 Writing to WTCNT and WTCSR
Содержание SH7709S
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Страница 292: ...273 T1 CKIO A25 to A0 CSn RD WR RD D31 to D0 WEn D31 to D0 BS T2 Read Write Figure 10 6 Basic Timing of Basic Interface ...
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