MITSUBISHI MICROCOMPUTERS
4280 Group
SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER for INFRARED REMOTE CONTROL TRANSMITTERS
WATCHDOG TIMER
Watchdog timer provides a method to reset and restart the system
when a program runs wild. Watchdog timer consists of 14-bit
timer (WDT) and watchdog timer flags (WDF1, WDF2).
Watchdog timer downcounts the instruction clock (INSTCK) as
the count source. When the timer WDT count value becomes
000016 and underflow occurs, the WDF1 flag is set to “1.” Then,
when the WRST instruction is not executed before the timer WDT
counts 16383, WDF2 flag is set to “1” and internal reset signal is
generated and system reset is performed.
When using the watchdog timer, execute the WRST instruction
at period of 16383 machine cycle or less to keep the
microcomputer operation normal.
Timer WDT is also used for generation of oscillation stabilization
time. When system is returned from reset and from RAM back-
up mode by key-input, software starts after the stabilization
oscillation time until timer WDT downcounts to 3E0016 elapses.
Software
start
Software
start
Software
start
3FFF16
3E0016
Value of timer WDT
0000 16
“1”
WDF1 flag
“0”
“1”
WDF2 flag
“0”
“H”
“L”
Internal reset signal
POF
instruction
execution
WRST
instruction
execution
System reset
System reset
Return
Fig. 14 Watchdog timer function
MITSUBISHI
ELECTRIC
13
MITSUBISHI [ Mitsubishi Group ]
