7540 datasheet(97/366 Pages) RENESAS

97 / 366 page

2-21

REJ09B0018-0200Z

Rev.2.00

Jun 21, 2004

7540 Group

APPLICATION

2.2 Timer A

(3) Application example of timer mode

Outline: The input clock is divided by the timer so that the period processing is executed every

25 ms intervals.

Specifications: •The f(XIN) = 8 MHz is divided by timer A to detect 25 ms.

•The timer A interrupt request is confirmed in the main routine. When 25 ms has

elapsed, the period processing is executed in the timer A interrupt processing

routine.

• Operation clock: f(XIN) = 8 MHz, high-speed mode

Figure 2.2.12 shows an example of control procedure.

Fig. 2.2.12 Example of control procedure

Set “0” to the timer A interrupt enable bit.

(Timer A interrupt disabled)

“D316”

“3016”

Timer A (low-order) (Address 1E16)

Set value to timer A (Notes 2, 3)

0 0

Set “0” to the timer A interrupt request bit.

CLI

TAM(Address 1D16)

Timer mode

Timer A count stop

Set timer A mode register

Initialization

RESET

SEI

CLD

CLT

CPUM(Address 3B16)

← 10000X002

Wait until f(XIN) oscillation is stabilized (Note 1)

CPUM(Address 3B16)

← 00000X002

Processing

Timer A interrupt processing routine

Periodic processing

RTI

Timer A (high-order) (Address 1F16)

Set “1” to the timer A interrupt enable bit.

(Timer A interrupt enabled)

TAM(Address 1D16)

Timer A count start

Set timer A mode register

X: This bit is not used here. Set it to “0” or “1” arbitrary.

Notes 1: For the concrete time, ask the oscillator manufacture.

2: When setting the value to Timer A, set in order of low-order

byte and high-order byte following.

3: 25 ms = 1/8 MHz ✕ 16 ✕ (30D316 + 1)

Timer A

division ratio

(fixed)

Timer A

setting value

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