7549 datasheet(36/86 Pages) RENESAS

36 / 86 page

Rev.2.02

Mar 31, 2009

Page 34 of 81

REJ03B0202-0202

7549 Group

Input capture

7549 group has 1-input capture channel and can be used to

capture count value of Timer A.

Input capture shares the registers with three output compare

channels, but their individual circuits operate independently so

that all the channels can be used at the same time.

To use input capture, set the capture

0 input port selection bits. If

P03 is selected, set the P03 direction register to 0. When an input

capture trigger is input to the input capture circuit, the count

value of timer A is saved to the capture latches. The timer count

value at the rising edge of the external input trigger is saved to

capture latch 00, and the timer count value at the falling edge of

the external input trigger is saved to capture latch 01. Capture

latch 00 and capture latch 01 can be read using the following

procedure.

1. Set the capture/compare register RW pointer to the read tar-

get address.

2. Read the high-order bits of the capture/compare registers,

then read the low-order bits of the capture/compare regis-

ters. (Read both the capture/compare registers in the

sequence of high-order bits followed by low-order bits.)

The count value of timer can be retained by software by capture

y (y = 00, 01, 10, 11) software trigger bit too. When “1” is set to

this bit, count value of timer is retained to the corresponded

capture latch.

When reading from the capture y software trigger bit is executed,

“0” is read out.

•Notes

• When the low-speed on-chip oscillator output or XCIN input

clock is selected as the count source of timer A, input capture

can be used only if the same clock source is selected as

φSOURCE and as the count source of timer A.

• When writing “1” to capture y software trigger bit of capture

latch 00 and 01 at the same time, or external trigger and

software trigger occur simultaneously, if capture latches 00

and 01 are input simultaneously, the set value of capture 0

status bit is undefined.

• When setting the interrupt active edge selection bit and noise

filter clock selection bit of capture 0 the interrupt request bit

may be set to “1”.

When not requiring the interrupt occurrence synchronized with

these setting, take the following sequence.

(1) Set the capture interrupt enable bit to “0” (disabled).

(2) Set the interrupt edge selection bit or noise filter clock

selection bit.

(3) Set the corresponding interrupt request bit to “0” after 1 or

more instructions have been executed.

(4) Set the capture interrupt enable bit to “1” (enabled).

• When the capture interrupt is used as the interrupt for return

from stop mode, set the capture 0 noise filter clock selection

bits to “00 (Filter stop)”.

Fig 40. Structure of capture software trigger register

Fig 41. Structure of capture mode register

Capture software trigger register

(CSTR: address 003116, initial value: 0016)

Capture latch 00 software trigger bit

Capture 00 software trigger occurs by setting “1”

to this bit. (returns “0” when read)

Capture latch 01 software trigger bit

Capture 01 software trigger occurs by setting “1”

to this bit. (returns “0” when read)

Not used (returns “0” when read)

Capture 0 interrupt edge selection bits

b1 b0

0 0 : Rising and falling edge

0 1 : Rising edge

1 0 : Falling edge

1 1 : Not available

Capture 0 noise filter clock selection bits

b1 b0

0 0 : Filter stop

0 1 : f (XIN)

1 0 : f (XIN)/8

1 1 : f (XIN)/32

Not used (returns “0” when read)

Capture mode register

(CAPM: address 003216, initial value: 0016)

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