4518 Datasheet, PDF (73/160 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4518 Group
15 _{Period measurement circuit}
When a period measurement circuit is used, clear bit 0 of regis-
ter I1 to “0”, and set a timer 1 count start synchronous circuit to
be “not selected”.
Start timer operation immediately after operation of a period
measurement circuit is started.
When the edge for measurement is input until timer operation is
started from the operation of period measurement circuit is
started, the count operation is not executed until the timer opera-
tion becomes valid. Accordingly, be careful of count data.
When data is read from timer, stop the timer and clear bit 2 of
register W5 to “0” to stop the period measurement circuit, and
then execute the data read instruction.
Depending on the state of timer 1, the timer 1 interrupt request
flag (T1F) may be set to “1” when the period measurement cir-
cuit is stopped by clearing bit 2 of register W5 to “0”. In order to
avoid the occurrence of an unexpected interrupt, clear the bit 2
of register V1 to “0” (refer to Figure 65➀) and then, stop the bit 2
of register W5 to “0” to stop the period measurement circuit.
In addition, execute the SNZT1 instruction to clear the T1F flag
after executing at least one instruction (refer to Figure 65➁).
Also, set the NOP instruction for the case when a skip is per-
formed with the SNZT1 instruction (refer to Figure 65➂).
While a period measurement circuit is operating, the timer 1 in-
terrupt request flag (T1F) is not set by the timer 1 underflow
signal, it is the flag for detecting the completion of period mea-
surement.
When a period measurement circuit is used, select the suffi-
ciently higher-speed frequency than the signal for measurement
for the count source of a timer 1.
When the signal for period measurement is D6/CNTR0 pin input,
do not select D6/CNTR0 pin input as timer 1 count source.
(The XIN input is recommended as timer 1 count source at the
time of period measurement circuit use.)
When the input of P30/INT0 pin is selected for measurement, set
the bit 3 of a register I1 to “1”, and set the input of INT0 pin to be
enabled.
LA 0
TV1A
LA 0
TW5A
NOP
SNZT1
NOP
; (✕0✕✕2)
; The SNZT1 instruction is valid ........ ➀
; (✕0✕✕2)
; Period measurement circuit stop
........................................................... ➁
; The SNZT1 instruction is executed
(T1F flag cleared)
........................................................... ➂
✕ : these bits are not used here.
Fig. 65 Period measurement circuit program example
Rev.3.01 2005.06.15 page 73 of 157
REJ03B0008-0301