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4501_M Datasheet, PDF (38/212 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 4500 SERIES | |||
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4501 Group
HARDWARE
FUNCTION BLOCK OPERATIONS
TIMERS
The 4501 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 â1,â 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 â1â after every n
count of a count pulse.
F F1 6
n : Counter initial value
Count starts
Reload
n
1st underflow
Reload
2nd underflow
0016
Timer interrupt â1â
request flag â0â
n+1 count
n+1 count
Time
An interrupt occurs or
a skip instruction is executed.
Fig. 21 Auto-reload function
The 4501 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.2.01 Feb 07, 2005
REJ09B0192-0201
1-26
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