SH7014 Datasheet, PDF (331/754 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

11. Watchdog Timer (WDT)
11.2.4 Register Access
The watchdog timer's TCNT, TCSR, and RSTCSR registers differ from other registers in that they
are more difficult to write to. The procedures for writing and reading these registers are given
below.
Writing to the TCNT and TCSR: These registers must be written by a word transfer instruction.
They cannot be written by byte transfer instructions.
The TCNT and TCSR both have the same write address. The write data must be contained in the
lower byte of the written word. The upper byte must be H'5A (for the TCNT) or H'A5 (for the
TCSR) (figure 11.2). This transfers the write data from the lower byte to the TCNT or TCSR.
Writing to the TCNT
15
Address: H'FFFF8610
H'5A
87
0
Write data
Writing to the TCSR
15
Address: H'FFFF8610
H'A5
87
0
Write data
Figure 11.2 Writing to the TCNT and TCSR
Writing to the RSTCSR: The RSTCSR must be written by a word access to address
H'FFFF8612. It cannot be written by byte transfer instructions.
Procedures for writing 0 in WOVF (bit 7) and for writing to RSTE (bit 6) are different, as shown
in figure 11.3.
To write 0 in the WOVF bit, the write data must be H'A5 in the upper byte and H'00 in the lower
byte. This clears the WOVF bit to 0. The RSTE bit is not affected. To write to the RSTE bit, the
upper byte must be H'5A and the lower byte must be the write data. The values of bit 6 of the
lower byte is transferred to the RSTE bit, respectively. The WOVF bit is not affected.
Rev.5.00 Sep. 27, 2007 Page 297 of 716
REJ09B0398-0500