HD64F2168 Datasheet, PDF (388/874 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer

13.6 Usage Notes
13.6.1 Notes on Register Access
The watchdog timer’s registers, TCNT and TCSR differ from other registers in being more
difficult to write to. The procedures for writing to and reading from these registers are given
below.
Writing to TCNT and TCSR (Example of WDT_0):
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, satisfy the relative condition
shown in figure 13.6 to write to TCNT or TCSR. To write to TCNT, the higher bytes must contain
the value H'5A and the lower bytes must contain the write data. To write to TCSR, the higher
bytes must contain the value H'A5 and the lower bytes must contain the write data.
<TCNT write>
15
Address : H'FFA8
H'5A
87
0
Write data
<TCSR write>
15
Address : H'FFA8
H'A5
87
0
Write data
Figure 13.6 Writing to TCNT and TCSR (WDT_0)
Reading from TCNT and TCSR (Example of WDT_0):
These registers are read in the same way as other registers. The read address is H'FFA8 for TCSR
and H'FFA9 for TCNT.
Rev. 3.00, 03/04, page 348 of 830