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ST9 USER GUIDE

4.3.1.5 Single/Continuous Mode

On counter underflow (End Of Count), the counter is always reloaded with the value of the

latch that is actually accessed when writing to the WDTHR and WDTLR register pair.

The counter has two modes: Single-shot or Continuous, selected by the S_C bit of WDTCR.

In Single-shot mode, the End Of Count also resets the ST_SP bit of the WDTCR, which stops

the counter after one cycle. In Continuous mode on reaching the End Of Count condition, the

counter reloads the constant and restarts. When the ST_SP bit is set, the contents of the latch

are written again to the counter, allowing the initial count value to be changed before starting

the counter.

You restart the down counter by setting the ST_SP bit. The constant value can be either the

initial value or a new one as shown on the following diagram:

Figure 32

. Timer in Single Mode

4.3.1.6 Output Pin

Another pin, WDOUT (alternate function of P5.1 for ST92F150), when enabled by the OUTEN

bit, can change its state in two ways on the end of count of the main counter. Basically, each

time the counter overflows, it updates the output value. This can produce two different effects,

selected by the OUTMD bit: either the state of the WROUT bit is copied to the output at that

time, or the output is complemented.

ST_SP

Counter

Value

Initial Value

End of Count

A new value may be written in the counter latches at any time. It will be transferred

into the counter on end of count or on various conditions on WDTIN and ST_SP.

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