h8s-2649 Renesas Electronics Corporation., h8s-2649 Datasheet - Page 385

• Manufacturer Part Number: h8s-2649
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2600 Series
• Manufacturer: Renesas Electronics Corporation.

12.5
12.5.1
The watchdog timer’s TCNT, TCSR, and RSTCSR registers differ from other registers in being
more difficult to write to. The procedures for writing to and reading these registers are given
below.
Writing to TCNT, TCSR, and RSTCSR
These registers must be written to by a word transfer instruction. They cannot be written to by a
byte transfer instruction.
TCNT and TCSR both have the same write address. Therefore, the relative condition shown in
figure 12.4 needs to be satisfied in order to write to TCNT or TCSR. The transfer instruction
writes the lower byte data to TCNT or TCSR according to the satisfied condition.
To write to RSTCSR, execute a word transfer instruction for address H'FF76. A byte transfer
instruction cannot write to RSTCSR.
The method of writing 0 to the WOVF bit differs from that of writing to the RSTE and RSTS bits.
To write 0 to the WOVF bit, satisfy the condition shown in figure 12.4. If satisfied, the transfer
instruction clears the WOVF bit to 0, but has no effect on the RSTE and RSTS bits. To write to
the RSTE and RSTS bits, satisfy the condition shown in figure 12.4. If satisfied, the transfer
instruction writes the values in bits 5 and 6 of the lower byte into the RSTE and RSTS bits,
respectively, but has no effect on the WOVF bit.
Figure 12.4 Writing to TCNT, TCSR, and RSTCSR (example for WDT0)
Usage Notes
Notes on Register Access
TCNT write
Writing to RSTE and RSTS bits
TCSR write
Writing 0 to WOVF bit
Address:
Address:
H'FF74
H'FF76
H'FF74
H'FF76
15
15
H'5A
H'A5
8
8
7
7
Write data or H'00
Rev. 2.00 Dec. 05, 2005 Page 347 of 724
Write data
Section 12 Watchdog Timer (WDT)
0
0
REJ09B0200-0200