4501_M Datasheet, PDF (138/212 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 4500 SERIES

4501 Group
APPLICATION
2.3 Timers
2.3 Timers
The 4501 Group has two 8-bit timers (each has a reload register) and a 16-bit fixed dividing frequency timer
which has the watchdog timer function.
This section describes individual types of timers, related registers, application examples using timers and
notes.
2.3.1 Timer functions
(1) Timer 1
s Timer operation
(Timer 1 has the timer 1 count start trigger function from P13/INT pin input)
(2) Timer 2
s Timer operation
(3) 16-bit timer
s Watchdog function
Watchdog timer provides a method to reset the system when a program run-away occurs.
System operates after it is released from reset. When the timer count value underflows, the WDF1
flag is set to “1.” Then, if the WRST instruction is never executed until timer WDT counts 65534,
WDF2 flag is set to “1,” and system reset occurs.
When the DWDT instruction and the WRST instruction are executed continuously, the watchdog timer
function is invalid.
The WRST instruction has the skip function. When the WRST instruction is executed while the WDF1
flag is “1”, the WDF1 flag is cleared to “0” and the next instruction is skipped.
Rev.2.01 Feb 07, 2005
REJ09B0192-0201
2-21