11.2.4
Register Access
The watchdog timer’s TCNT and TCSR registers are more difficult to write to than other registers.
The procedures for writing and reading these registers are given below.
Writing to TCNT and TCSR: Word access is required. Byte data transfer instructions cannot be
used for write access.
The TCNT and TCSR registers have the same write address. The write data must be contained in
the lower byte of a word written at this address. The upper byte must contain H'5A (password for
TCNT) or H'A5 (password for TCSR). See figure 11.2. The result of the access depicted in figure
11.2 is to transfer the write data from the lower byte to TCNT or TCSR.
15
8 7
0
Writing to TCNT
Address H'FFA8
H'5A
H'A5
Write data
Write data
15
8 7
0
Writing to TCSR
Address H'FFA8
Figure 11.2 Writing to TCNT and TCSR
Reading TCNT and TCSR: The read addresses are H'FFA8 for TCSR and H'FFA9 for TCNT, as
indicated in table 11.2.
These two registers are read like other registers. Byte access instructions can be used.
Table 11.2 Read Addresses of TCNT and TCSR
Read Address
H'FFA8
Register
TCSR
H'FFA9
TCNT
228
RENESAS [ RENESAS TECHNOLOGY CORP ]
