4502 Datasheet, PDF (24/116 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4502 Group
TIMERS
The 4502 Group has the following timers.
• Programmable timer
The programmable timer has a reload register and enables the
frequency dividing ratio to be set. It is decremented from a set-
ting value n. When it underflows (count to n + 1), a timer interrupt
request flag is set to “1,” new data is loaded from the reload reg-
ister, and count continues (auto-reload function).
• Fixed dividing frequency timer
The fixed dividing frequency timer has the fixed frequency divid-
ing ratio (n). An interrupt request flag is set to “1” after every n
count of a count pulse.
FF16
n : Counter initial value
Count starts
Reload
n
1st underflow
Reload
2nd underflow
0016
Timer interrupt ^{“1”}
request flag ^{“0”}
n+1 count
n+1 count
Time
An interrupt occurs or
a skip instruction is executed.
Fig. 21 Auto-reload function
The 4502 Group timer consists of the following circuits.
• Prescaler : frequency divider
• Timer 1 : 8-bit programmable timer
• Timer 2 : 8-bit programmable timer
(Timers 1 and 2 have the interrupt function, respectively)
• 16-bit timer
Prescaler and timers 1 and 2 can be controlled with the timer con-
trol registers W1, W2 and W6. The 16-bit timer is a free counter
which is not controlled with the control register.
Each function is described below.
Table 9 Function related timers
Circuit
Structure
Count source
Prescaler
Timer 1
Timer 2
16-bit timer
Frequency divider
• Instruction clock
8-bit programmable • Prescaler output (ORCLK)
binary down counter
(link to INT input)
8-bit programmable • Timer 1 underflow
binary down counter • Prescaler output (ORCLK)
• CNTR input
• System clock
16-bit fixed dividing • Instruction clock
frequency binary down
counter
Frequency
dividing ratio
4, 16
1 to 256
1 to 256
65536
Use of output signal
• Timer 1 and 2 count sources
• Timer 2 count source
• CNTR output
• Timer 1 interrupt
• CNTR output
• Timer 2 interrupt
• Watchdog timer
(The 16th bit is counted twice)
Control
register
W1
W1
W2
W6
W2
W6
Rev.3.01 2005.02.02 page 24 of 112
REJ03B0105-0301