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M37640E8FP

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

Mitsumi 

Ver 1.4

MITSUBISHI MICROCOMPUTERS

7640 Group

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

1.17.4 Timer 2

1.17.5 Timer 3

Timer 2 is an 8-bit timer with an 8-bit reload latch (see

Figure 1.35).

T123M7 (bit 7 of T123M) is the Timer 1 and 2 Data

Write Control Bit. If T123M7 is “1”, data written to

Timer 2 is placed only in the Timer 2 reload latch (see

Figure 1.32). The latch value is loaded into Timer 2

after Timer 2 underflows. If the T123M7 is “0”, the

value written to Timer 2 is placed in Timer 2 and the

Timer 2 reload latch. At reset, T123M2 is set to a “0”.

The Timer 2 reload latch value is not affected by a

change of the count source. However, because

changing the count source may cause an inadvertent

countdown of the timer, the timer should be rewritten

when the count source is changed.

•Timer Mode

Count Source:

•If T123M3 is “0”, the Timer 2 count source is the

Timer 1 underflow output.

•If T123M3 is “1”, the Timer 2 count source is F.

In Timer mode, each time the timer underflows, the

corresponding timer interrupt request bit is set to a

“1”, the contents of the timer latch are loaded into

the timer, and the count down sequence begins

again.

•Pulse Output Mode

Count Source:

•If T123M3 is “0”, the Timer 2 count source is the

Timer 1 underflow output.

•If T123M3 is “1”, the Timer 2 count source is F.

Timer 2 Pulse Output mode is enabled by setting

T123M6 to a “1” and T123M0 to a “1”. Each time the

Timer 2 underflows, the output of the TOUT pin is

inverted, and the corresponding Timer 2 interrupt

request bit is set to a “1”. The repeated inversion of

the TOUT pin output produces a rectangular wave-

form with a duty ratio of 50 percent. The initial level

of the output is determined by the TOUT polarity se-

lect bit (T123M5). When this bit is “0”, the output

starts from a high level. When this bit is “1”, the out-

put starts from a low level.

Timer 3 is an 8-bit timer with an 8-bit reload latch (see

Figure 1.35). The Timer 3 reload latch value is not af-

fected by a change of the count source. Because

changing the count source may cause an inadvertent

countdown of the timer, the timer should be rewritten

whenever the count source is changed.

•Timer Mode

Count Source:

•If T123M4 is “0”, the Timer 3 count source is the

Timer 1 underflow output.

•If T123M4 is “1”, the count source is F/8

In Timer mode, each time the timer underflows, the

corresponding timer interrupt request bit is set to a

“1”, the contents of the timer latch are loaded into the

timer, and the count down sequence begins again.

Data written to Timer 3 is always placed in Timer 3

and the Timer 3 reload latch.

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