HD6412320 RENESAS [Renesas Technology Corp], HD6412320 Datasheet - Page 618

• Manufacturer Part Number: HD6412320
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family H8S-2300 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

Section 13 Watchdog Timer
Bit 5—Reserved: This bit should be written with 0.
Bits 4 to 0—Reserved: These bits cannot be modified and are always read as 1.
13.2.4
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 and TCSR: These registers must be written to by a word transfer instruction.
They cannot be written to with byte instructions.
Figure 13.2 shows the format of data written to TCNT and TCSR. TCNT and TCSR both have the
same write address. For a write to TCNT, the upper byte of the written word must contain H'5A
and the lower byte must contain the write data. For a write to TCSR, the upper byte of the written
word must contain H'A5 and the lower byte must contain the write data. This transfers the write
data from the lower byte to TCNT or TCSR.
Writing to RSTCSR: RSTCSR must be written to by a word transfer instruction to address
H'FFBE. It cannot be written to with byte instructions.
Figure 13.3 shows the format of data written to RSTCSR. The method of writing 0 to the WOVF
bit differs from that for writing to the RSTE bit.
To write 0 to the WOVF bit, the write data must have H'A5 in the upper byte and H'00 in the
lower byte. This clears the WOVF bit to 0, but has no effect on the RSTE bit. To write to the
RSTE bit, the upper byte must contain H'5A and the lower byte must contain the write data. This
writes the value in bit 6 of the lower byte into the RSTE bit, but has no effect on the WOVF bit.
Rev.6.00 Sep. 27, 2007 Page 588 of 1268
REJ09B0220-0600
TCNT write
TCSR write
Notes on Register Access
Address: H'FFBC
Address: H'FFBC
Figure 13.2 Writing to TCNT and TCSR
15
15
H'5A
H'A5
8 7
8 7
Write data
Write data
0
0