Notes On Register Access; Figure 10.3 Writing To Wtcnt And Wtcsr - Hitachi SH7751 Hardware Manual

10.8.3

Notes on Register Access

The watchdog timer counter (WTCNT) and watchdog timer control/status register (WTCSR)
differ from other registers in being more difficult to write to. The procedure for writing to these
registers is given below.
Writing to WTCNT and WTCSR: These registers must be written to with a word transfer
instruction. They cannot be written to with a byte or longword transfer instruction. When writing
to WTCNT, perform the transfer with the upper byte set to H'5A and the lower byte containing the
write data. When writing to WTCSR, perform the transfer with the upper byte set to H'A5 and the
lower byte containing the write data. This transfer procedure writes the lower byte data to
WTCNT or WTCSR. The write formats are shown in figure 10.3.
WTCNT write
Address: H'FFC00008
(H'1FC00008)
WTCSR write
Address: H'FFC0000C
(H'1FC0000C)
15
H'5A
15
H'A5

Figure 10.3 Writing to WTCNT and WTCSR

8 7
Write data
8 7
Write data
Rev. 3.0, 04/02, page 257 of 1064
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