Watchdog Timer Operation States - Hitachi H8/3937 Series Hardware Manual

Figure 9-18 shows an example of watchdog timer operations.
Example: ø = 2 MHz and the desired overflow period is 30 ms.
The value set in TCW should therefore be 256 – 8 = 248 (H'F8).
H'FF
H'F8
TCW count
value
H'00
H'F8 written
in TCW
Internal reset
signal
Figure 9-18 Typical Watchdog Timer Operations (Example)
9.6.4

Watchdog Timer Operation States

Table 9-18 summarizes the watchdog timer operation states.
Table 9-18 Watchdog Timer Operation States
Operation
Mode Reset
TCW Reset
TCSRW Reset
Note: * Functions when øw/32 is selected as the input clock.
2 × 10
6
× 30 × 10
8192
Start
H'F8 written in TCW
Active Sleep Watch
Functions Functions Halted
Functions Functions Retained
–3
= 7.3
512 ø
Subactive Subsleep Standby
Functions/ Halted
Halted*
Functions/ Retained
Halted*
TCW overflow
Reset
clock cycles
OSC
Module
Standby
Halted Halted
Retained Retained
239