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TIMER A

7721 Group User’s Manual

8–24

8.4 Event counter mode

8.4.3 Switching between countup and countdown

The up-down register (address 4416) or the input signal from the TAjOUT pin is used to switch countup from

and to countdown. This switching is performed by the up-down bit when the up-down switching factor select

bit (bit 4 at addresses 5816 to 5A16) is “0,” and by the input signal from the TAjOUT pin when the up-down

switching factor select bit is “1.”

When the switching between countup and countdown is set while counting is in progress, this switching is

actually performed when the count source’s next valid edge is input.

(1)

Switching by up-down bit

Countdown is performed when the up-down bit is “0,” and countup is performed when the up-down

bit is “1.” Figure 8.4.5 shows the structure of the up-down register.

(2)

Switching by TAjOUT pin’s input signal

Countdown is performed when the TAjOUT pin’s input signal is at “L” level, and countup is performed

when the TAjOUT pin’s input signal is at “H” level.

When using the TAjOUT pin’s input signal to switch countup from and to countdown, set the port P5

direction register’s bit which corresponds to the TAjOUT pin for the input mode.

Fig. 8.4.5 Structure of up-down register

Bit

Bit name

At reset

Functions

Up-down register (Address 4416)

Timer A4 up-down bit

Timer A3 up-down bit

Timer A2 up-down bit

Fix these bits to “0.”

Timer A2 two-phase pulse signal

processing select bit

(Note)

Timer A3 two-phase pulse signal

processing select bit

(Note)

Timer A4 two-phase pulse signal

processing select bit

(Note)

0 : Countdown

1 : Countup

This function is valid when the contents of

the up-down register is selected as the up-

down switching factor.

0 : Two-phase pulse signal

processing function disabled

1 : Two-phase pulse signal

processing function enabled

When not using the two-phase pulse

signal processing function, set the bit

to “0.”

The value is “0” at reading.

Note: Use the LDM or STA instruction for writing to bits 5 to 7.

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