4570 Datasheet, PDF (25/69 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

(6) Timer 3
Timer 3 is an 8-bit binary down counter with the timer 3 reload
registers (R3H, R3L). Data can be set simultaneously in timer
3 and the reload register (R3L) with the T3AB instruction.
Data can be set in reload register R3H with the T3HAB
instruction.
Timer 3 starts counting after the following process;
Πset data in timer 3,
 select the count source with the bits 1 and 0 of register
W3,
Ž set the bit 3 of register W3 to “1.”
The f(XIN) or f(XIN)/2 is selected as the count source by setting
W31 to “1” and W30 to “0.”
When the f(XIN) is selected as the system clock (bit 3 of clock
control register MR= “0”), f(XIN) is selected as the count
source.
When the f(XIN)/4 is selected as the system clock (bit 3 of
clock control register MR= “1”), f(XIN)/2 is selected as the
count source.
Once count is started, when timer 3 underflows (the next count
pulse is input after the contents of timer 3 become “0”), the
timer 3 interrupt request flag (T3F) is set to “1,” new data is
loaded from reload register R3H, and count coutinues (auto-
reload function).
When the timer 3 underflows again after auto-reload is
performed, the timer 3 interrupt request flag (T3F) is set to
“1” and new data is reloaded from the reload register R3L
and count continues. Timer 3 reloads data from reload register
R3H or R3L alternately every underflow.
When the T3AB instruction is executed while timer 3 is
operating, new data is set in timer 3 and reload register R3L,
count is started again at the next machine cycle. At the next
underflow, data is reloaded from R3H and count continues
regardless that auto-reload is performed from reload register
R3H or R3L at the previous underflow.
Data can be read from timer 3 through registers A and B.
Stop counting and then execute the TAB3 instruction to read
its data. Timer 3 can be also used as the carrier wave
generating circuit.
(7) Timer output pin (D9/TOUT)
Timer output pin (D9/TOUT) is used to output the timer 2
underflow signal.
The D9/TOUT pin function can be selected by the bit 2 of register
W2.
(8) Timer interrupt request flags (T1F, T2F, T3F)
Each timer interrupt request flag is set to “1” when each timer
underflows. The state of these flags can be examined with
the skip instructions (SNZT1, SNZT2, SNZT3).
Use the interrupt control registers V1 and V2 to select an
interrupt or a skip instruction.
An interrupt request flag is cleared to “0” when an interrupt
occurs or when the next instruction is skipped with a skip
instruction.
MITSUBISHI MICROCOMPUTERS
4570 Group
SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER
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