SH7058 Datasheet, PDF (485/1130 Pages) Renesas Technology Corp – Renesas SuperHTM RISC engine

Writing 0 to the WOVF bit
15
87
0
Address: H'FFFFEC12
H'A5
H'00
Writing to the RSTE and RSTS bits
15
Address: H'FFFFEC12
H'5A
87
0
Write data
Figure 13.3 Writing to RSTCSR
Reading from TCNT, TCSR, and RSTCSR: TCNT, TCSR, and RSTCSR are read like other
registers. Use byte transfer instructions. The read addresses are H'FFFFEC10 for TCSR,
H'FFFFEC11 for TCNT, and H'FFFFEC13 for RSTCSR.
13.3 Operation
13.3.1 Watchdog Timer Mode
To use the WDT as a watchdog timer, set the WT/IT and TME bits in TCSR to 1. Software must
prevent TCNT overflow by rewriting the TCNT value (normally by writing H'00) before overflow
occurs. No TCNT overflows will occur while the system is operating normally, but if TCNT fails
to be rewritten and overflows occur due to a system crash or the like, a WDTOVF signal is output
externally (figure 13.4). The WDTOVF signal can be used to reset the system. The WDTOVF
signal is output for 128 φ clock cycles.
If the RSTE bit in RSTCSR is set to 1, a signal to reset the chip will be generated internally
simultaneous with the WDTOVF signal when TCNT overflows. Either a power-on reset or a
manual reset can be selected by the RSTS bit in RSTCSR. The internal reset signal is output for
512 φ clock cycles.
When a WDT overflow reset is generated simultaneously with a reset input at the RES pin, the
RES reset takes priority, and the WOVF bit in RSTCSR is cleared to 0.
The following registers are not initialized by a WDT reset signal:
• PFC (pin function controller) registers
• I/O port registers
These registers are initialized only by an external power-on reset.
Rev. 3.0, 09/04, page 444 of 1086