R8C datasheet(73/199 Pages) RENESAS

73 / 199 page

R8C/10 Group

Rev.1.20 Jan 27, 2006

page 63 of 180

REJ09B0019-0120

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.

Item

Specification

Count source

f1, f2, f8, f32

Count operation

• 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.

Count start condition

Write “1” (count start) to TXS bit in TXMR register

Count stop condition

Write “0” (count stop) to TXS bit in TXMR register

Interrupt request

• 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

_______

Measurement pulse input(1) (INT1 interrupt input)

CNTR0 pin function

Programmable I/O port

Read from timer

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.

Write to timer

Value written to TX register is written to both reload register and counter.

Same applies to PREX register.

Select function

• INT1/CNTR0 polarity switching function

Measurement period of input pulse can be selected with R0EDG bit.

NOTES:

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.

Table 12.6 Pulse Period Measurement Mode Specifications

Timer X mode register

Symbol

Address

After reset

TXMR

008B16

0016

Bit name

Function

Bit symbol

b7 b6 b5 b4 b3 b2 b1 b0

0 0 : Timer mode or pulse period

measurement mode

b1 b0

TXMOD1

R0EDG

TXMOD0

INT1/CNTR0

polarity

switching bit(1)

Operation mode

select bit 0, 1

0 0

TXMOD2

TXS

TXOCNT

Timer X count

start flag

0 : Stops counting

1 : Starts counting

Operation mode

select bit 2

1 : Pulse period measurement mode

Set to “0” in pulse period measurement mode

TXEDG(2)

TXUND(2)

Timer X

underflow flag

0 : No under flow

1 : Under flow found

0 : No active edge

1 : Active edge found

Active edge

judgment 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”)

[CNTR0]

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]

0: Rising edge

1: Falling edge

Figure 12.9 TXMR Register in Pulse Period Measurement Mode

12.1 Timer (Timer X)

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