Renesas SH7041 Series, Hardware Manual, Page: 499 / 923

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13.2.4Register 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 13.2). This transfers the write data from the lower byte to the TCNT or TCSR.
H'5A H'FFFF8610 Address:
Writing to the TCNT
15 8 7 0
Write data
H'A5 H'FFFF8610 Address:
Writing to the TCSR
15 8 7 0
Write data
Figure 13.2 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) and RSTS (bit 5) are
different, as shown in figure 13.3.
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 and RSTS bits are not affected. To write to the
RSTE and RSTS bits, the upper byte must be H'5A and the lower byte must be the write data. The
values of bits 6 and 5 of the lower byte are transferred to the RSTE and RSTS bits, respectively.
The WOVF bit is not affected.