576
15.3
Operation
15.3.1
Watchdog Timer Operation
To use the WDT as a watchdog timer, set the WT/
IT
bit in TCSR and TME bit to 1. Software
must prevent TCNT overflows by rewriting the TCNT value (normally be writing H'00) before
overflows occurs. This ensures that TCNT does not overflow while the system is operating
normally. If TCNT overflows without being rewritten because of a system crash or other error, in
the WDT0 the
WDTOVF
signal is output. This is shown in figure 15-4. This
WDTOVF
signal can
be used to reset the system. The
WDTOVF
signal is output for 132 states when RSTE = 1, and for
130 states when RSTE = 0.
If TCNT overflows when 1 is set in the RSTE bit in RSTCSR, a signal that resets the H8S/2633
Series internally is generated at the same time as the
WDTOVF
signal. This reset can be selected
as a power-on reset or a manual reset, depending on the setting of the RSTS bit in RSTCSR. The
internal reset signal is output for 518 states.
If a reset caused by a signal input to the
RES
pin occurs at the same time as a reset caused by a
WDT overflow, the
RES
pin reset has priority and the WOVF bit in RSTCSR is cleared to 0.
In the case of WDT1, the chip is reset, or an NMI interrupt request is generated, for 516 system
clock periods (516ø) (515 or 516 states when the clock source is øSUB (PSS = 1)). This is
illustrated in figure 15-4 (b).
An NMI request from the watchdog timer and an interrupt request from the NMI pin are both
treated as having the same vector. So, avoid handling an NMI request from the watchdog timer
and an interrupt request from the NMI pin at the same time.
Содержание H8S/2631
Страница 28: ...xviii Appendix G Package Dimensions 1154 ...
Страница 341: ...316 Transfer SAR or DAR DAR or SAR Block area First block Nth block Figure 9 8 Memory Mapping in Block Transfer Mode ...
Страница 918: ...905 ø DREQ0 DREQ1 tDRQS tDRQH Figure 25 19 DMAC DREQ Input Timing ...
Страница 955: ...943 A 2 Instruction Codes Table A 2 shows the instruction codes ...