CHAPTER 10 WATCHDOG TIMER
User’s Manual U16899EJ2V0UD
235
Cautions 1. If data is written to WDTM, a wait cycle is generated. Do not write data to WDTM
when the CPU is operating on the subsystem clock and the high-speed system clock
is stopped. For details, see CHAPTER 32 CAUTIONS FOR WAIT.
2. Set bits 7, 6, and 5 to 0, 1, and 1, respectively (when “Ring-OSC cannot be stopped”
is selected by the option byte, other values are ignored).
3. After reset is released, WDTM can be written only once by an 8-bit memory
manipulation instruction. If writing attempted a second time, an internal reset signal
is generated. If the source clock to the watchdog timer is stopped, however, an
internal reset signal is generated when the source clock to the watchdog timer
resumes operation.
4. WDTM cannot be set by a 1-bit memory manipulation instruction.
5. If “Ring-OSC can be stopped by software” is selected by the option byte and the
watchdog timer is stopped by setting WDCS4 to 1, the watchdog timer does not
resume operation even if WDCS4 is cleared to 0. In addition, the internal reset signal
is not generated.
Remarks 1. f
R
: Ring-OSC clock oscillation frequency
2. f
XP
: High-speed system clock oscillation frequency
3.
×
: Don’t care
4. Figures in parentheses apply to operation at f
R
= 480 kHz (MAX.), f
XP
= 10 MHz
(2) Watchdog timer enable register (WDTE)
Writing ACH to WDTE clears the watchdog timer counter and starts counting again.
This register can be set by an 8-bit memory manipulation instruction.
RESET input sets this register to 9AH.
Figure 10-3. Format of Watchdog Timer Enable Register (WDTE)
0
1
2
3
4
5
6
7
Symbol
WDTE
Address: FF99H After reset: 9AH R/W
Cautions 1. If a value other than ACH is written to WDTE, an internal reset signal is generated. If
the source clock to the watchdog timer is stopped, however, an internal reset signal
is generated when the source clock to the watchdog timer resumes operation.
2. If a 1-bit memory manipulation instruction is executed for WDTE, an internal reset
signal is generated. If the source clock to the watchdog timer is stopped, however,
an internal reset signal is generated when the source clock to the watchdog timer
resumes operation.
3. The value read from WDTE is 9AH (this differs from the written value (ACH)).
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