R8C/1A Group, R8C/1B Group 14. Timers
Rev.1.30 Dec 08, 2006 Page 116 of 315
REJ09B0252-0130
14.1.4 Pulse Width Measurement Mode
In pulse width measurement mode, the pulse width of an external signal input to the INT1/CNTR0 pin is
measured (refer to Table 14.5 Pulse Width Measurement Mode Specifications). Figure 14.7 shows the
TXMR Register in Pulse Width Measurement Mode. Figure 14.8 shows an Operating Example in Pulse Width
Measurement Mode.
Table 14.5 Pulse Width Measurement Mode Specifications
Item Specification
Count sources f1, f2, f8, fRING
Count operations • Decrement
• Continuously counts the selected signal only when the measured pulse is “H”
level, or conversely only “L” level.
• When the timer underflows, the contents of the reload register are reloaded
and the count is continued.
Count start condition 1 (count starts) is written to the TXS bit in the TXMR register.
Count stop condition 0 (count stops) is written to the TXS bit in the TXMR register.
Interrupt request
generation timing
• When timer X underflows [timer X interrupt].
• Rising or falling of the CNTR0 input (end of measurement period) [INT1
interrupt]
INT10
/CNTR00,
INT11
/CNTR01
pin functions
Measured pulse input
(INT1
interrupt input)
CNTR0
pin function
Programmable I/O port
Read from timer The count value can be read out by reading registers TX and PREX.
Write to timer • When registers TX and PREX are written while the count is stopped, values
are written to both the reload register and counter.
• When registers TX and PREX are written during the count, the value is written
to each reload register of registers TX and PREX at the following count source
input, the data is transferred to the counter at the second count source input,
and the count re-starts at the third count source input.
Select functions
•INT1
/CNTR0 signal polarity switch function
The R0EDG bit can select “H” or “L” level period for the input pulse width
measurement.
• Measured pulse input pin select function
The CNTRSEL bit in the UCON register can select the CNTR00 or CNTR01
pin.
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