R8C/13 Group
12.1 Timer (Timer X)
12.1.5 Pulse Period Measurement Mode
In this mode, the timer measures the pulse period of an external signal fed to INT1/CNTR0 pin (See
“Table 12.6 Pulse Period Measurement Mode Specifications”). Figure 12.9 shows the TXMR register
in pulse period measurement mode. Figure 12.10 shows an operation example in pulse period mea-
surement mode.
Table 12.6 Pulse Period Measurement Mode Specifications
Item
Count source
Count operation
Specification
f1, f2, f8, f32
• Down-count
• After an active edge of measurement pulse is input, contents in the read-out buffer is
retained in the first underflow of prescaler X. Then the timer X reloads contents in the
reload register in the second underflow of prescaler X and continues counting.
Write “1” (count start) to TXS bit in TXMR register
Count start condition
Count stop condition
Interrupt request
Write “0” (count stop) to TXS bit in TXMR register
• When Timer X underflows or reloads [Timer X interrupt]
_____
generation timing
• Rising or falling of CNTR0 input (end of measurement period) [INT1 interrupt]
_______
INT1/CNTR0 pin function
CNTR0 pin function
Read from timer
Measurement pulse input(1)(INT1 interrupt input)
Programmable I/O port
Contents in the read-out buffer can be read by reading TX register. The value retained in
the read-out buffer is released by reading TX register.
Value written to TX register is written to both reload register and counter.
Write to timer
Select function
NOTES:
Same applies to PREX register.
_____
• INT1/CNTR0 polarity switching function
Measurement period of input pulse can be selected with R0EDG bit.
1. The period of input pulse must be longer than twice the period of prescaler X. Longer pulse for H width and L width than
the prescaler X period must be input. If shorter pulse than the period is input to the CNTR0 pin, the input may be disabled.
Timer X mode register
b7 b6 b5 b4 b3 b2 b1 b0
Symbol
TXMR
Address
008B16
After reset
0016
0
0
1
0
Bit symbol
TXMOD0
TXMOD1
Function
Bit name
RW
RW
RW
b1 b0
Operation mode
select bit 0, 1
0 0 : Timer mode or pulse period
measurement mode
[CNTR0]
INT1/CNTR0
polarity
switching bit(1)
R0EDG
0: Measures a measurement pulse from one
rising edge to the next rising edge
1: Measures a measurement pulse from one
falling edge to the next falling edge
[INT1]
RW
0: Rising edge
1: Falling edge
Timer X count
start flag
0 : Stops counting
1 : Starts counting
TXS
RW
RW
RW
RW
RW
Set to “0” in pulse period measurement mode
TXOCNT
TXMOD2
Operation mode
select bit 2
1 : Pulse period measurement mode
0 : No active edge
1 : Active edge found
Active edge
judgment flag
TXEDG(2)
TXUND(2)
0 : No under flow
1 : Under flow found
Timer X
underflow flag
NOTES:
1. The IR bit in the INT1IC register may be set to “1” (interrupt requested) when the R0EDG bit is rewritten.
Refer to the paragraph 19.2.5 “Changing Interrupt Factor” in the Usage Notes Reference Book.
2. This bit is set to “0” by writing “0” in a program. (It remains unchanged even if writing “1”)
Figure 12.9 TXMR Register in Pulse Period Measurement Mode
Rev.1.20 Jan 27, 2006 page 78 of 205
REJ09B0111-0120
RENESAS [ RENESAS TECHNOLOGY CORP ]
