R8CSLASH15 datasheet(252/277 Pages) RENESAS

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R8C/14 Group, R8C/15 Group

20. Precautions

Rev.2.10

Jan 19, 2006

Page 240 of 253

REJ09B0164-0210

20.4

Timers

20.4.1

Timers X and Z

• Timers X and Z stop counting after reset. Set the value to these timers and prescalers before the

count starts.

• Even if the prescalers and timers are read out in 16-bit units, these registers are read by 1 byte in

the microcomputer. Consequently, the timer value may be updated during the period these two

registers are being read.

20.4.2

Timer X

• Do not rewrite the TXMOD0 to TXMOD1 bits, the TXMOD2 and TXS bits simultaneously.

• In pulse period measurement mode, the TXEDG bit and TXUND bit in the TXMR register can be

set to “0” by writing “0” to these bits by a program. However, these bits remain unchanged when

“1” is written. When using the READ-MODIFY-WRITE instruction for the TXMR register, the

TXEDG or TXUND bit may be set to “0” although these bits are set to while the instruction is

executed. At the time, write “1” to the TXEDG or TXUND bit which is not supposed to be set to “0”

with the MOV instruction.

• When changing to pulse period measurement mode from other mode, the contents of the TXEDG

and TXUND bits are indeterminate. Write “0” to the TXEDG and TXUND bits before the count

starts.

• The TXEDG bit may be set to “1” by the prescaler X underflow which is generated for the first

time since the count starts.

• When using the pulse period measurement mode, leave two periods or more of the prescaler X

immediately after count starts, and set the TXEDG bit to “0”.

• The TXS bit in the TXMR register has a function to instruct Timer X to start or stop counting, and

a function to indicate the count starts or stops.

“0” (count stops) can be read until the following count source is applied after “1” (count starts) is

written to the TXS bit while the count is being stopped. If the following count source is applied, “1”

can be read from the TXS bit. Do not access registers associated with Timer X (TXMR, PREX,

TX, TCSS, TXIC registers) except for the TXS bit until “1” can be read from the TXS bit. The

count starts at the following count source after the TXS bit is set to “1”.

Also, when writing “0” (count stops) to the TXS bit during the count, Timer X stops counting at the

following count source.

“1” (count starts) can be read by reading the TXS bit until the count stops after writing “0” to the

TXS bit. Do not access registers associated with Timer X other than the TXS bit until “0” can be

read by the TXS bit after writing “0” to the TXS bit.

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