7480 datasheet(109/337 Pages) RENESAS

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7480 Group and 7481 Group User's Manual

1-92

1.12 Timer X and Timer Y

HARDWARE

1.12.11 Notes on Usage

Pay attention to the following notes when timer X or Y is used.

(1)

In All Modes

Write to and Read from Timers

Write to and read from each timer two bytes together in the following order:

• Write: low-order byte

→ high-order byte

• Read: high-order byte

→ low-order byte

When a read from and a write into the same timer are executed during an interrupt service routine

etc., the normal operation cannot be performed.

In the pulse period measurement mode and the pulse width measurement mode, do not write to

timers.

Writes to Timers

When the timer X or Y write control bit is ‘0’:

• A write to an operating timer causes the contents of the timer to be affected, so that the time from

the last underflow until the next underflow is undefined in this case.

• A write to the low-order byte of an operating timer allows the timer to continue counting down until

the next write to the high-order byte. Therefore, the time until the subsequent underflow may be

undefined.

Figure 1.12.27 shows an operation in timer X or timer Y at writes.

Count source

• Example: Writing ‘020016’ into timer

Undefined value

0016

FF16

FE16

FD16

0216

‘0016’ is written to the

low-order of timer

‘0216’ is written to the

high-order of timer

Contents of timer (low-order)

Contents of timer (high-order)

Note: In this case, the write control bit is ‘0’.

Figure 1.12.27 Operation in Timer X or Timer Y at Writes

When the timer X or Y write control bit is ‘1’:

• A write to a stopped timer causes the contents of the timer not to be affected and allows the timer

to count down from the value prior to this write. Therefore, the time from the start of count down

until the first underflow is undefined.

• If a write and an underflow occur at approximately the same time in an operating timer, the reloaded

value may be undefined.

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