7549 datasheet(29/84 Pages) RENESAS

29 / 84 page

Rev.2.01

Oct 15, 2007

Page 29 of 81

REJ03B0202-0201

7549 Group

Timer A (TA)

Timer A is a 16-bit timer and counts the signal selected by the

timer A count source selection bit.

The count source of Timer A can be selected from among

φSOURCE/2, /16, /32, /64, /128, /256, low-speed on-ship

oscillator clock, and XCIN input clock.

Timer A counts the selected count source and sets the timer A

interrupt request bit to “1”.

When writing to timer A, the setting value of the timer A write

control bit can be used to select a write to both the timer A latch

and timer or a write to only the timer A latch.

Reading from timer A reads the timer A count value.

Be sure to write to and read from the low-order and the higher

order of timer A in the following order:

•Read

Read the high-order of Timer A (TAH) first, and the low-

order of Timer A (TAL) next. Always read both of the

registers.

• Write

Write to the low-order of Timer A (TAL) first and the

high-order of Timer A next. Always read both of the

registers.

Counting starts from “FFFF16” after reset.

The division ratio of timer A is 1/(n+1), where n is the timer A

setting value. Timer A stops when the timer A count stop bit is

set to “1”.

Timer A can be used as the timing timer for input capture and

output compare functions.

•Notes

(1) Timer Value Setting

When the timer A write control bit is set to “write to only latch”,

written data is written to only to the latch even when the timer is

stopped. To set the initial setting value when the timer is stopped,

select “Write to timer and latch simultaneously” beforehand.

(2) Reading from and Writing to Timer A

If the timer A count source clock and

φSOURCE are different

clocks, timer A cannot be read or written during its counting.

Select the same clock or set timer A to stop counting to enable

read and write operations.

• Timer A cannot be read/written in the following conditions:

Timer A count source: XCIN input clock

φSOURCE: Clock other than XCIN input clock

Timer A count source: Low-speed on-chip oscillator output

φSOURCE: Clock other than low-speed on-chip oscillator

(3) Count Source of Timer A

The XCIN input clock can be selected as the count source of timer

A only if the 32 kHz quartz crystal oscillator is selected by the

oscillation method selection bit in FSROM1.

Fig 28. Block diagram of timer A

Data bus

Low-speed on-chip

oscillator output

φSOURCE/256

φSOURCE/128

φSOURCE/64

φSOURCE/32

φSOURCE/16

φSOURCE/2

Timer A (low-order) latch (8)

XCIN input clock

(32 kHz quart

crystal oscillator)

Timer A (high-order) latch (8)

Timer A (low-order) (8)

Timer A (high-order) (8)

Timer A write

control bit

Timer A interrupt

request

Compare

Capture

Timer A count

stop bit

Timer A

count source

selection bits

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