9.3.7.7 USART Comparison Function on Received Character

The comparison function differs if the asynchronous partial wakeup is enabled or not.

If the asynchronous partial wakeup is disabled, the CMP flag in FLEX_US_CSR is set when the received character matches the conditions programmed in FLEX_US_CMPR. The CMP flag is set as soon as FLEX_US_RHR is loaded with the new received character. The CMP flag is cleared by writing a one to FLEX_US_CR.RSTSTA.

FLEX_US_CMPR can be programmed to provide different comparison methods:

• If VAL1 equals VAL2, then the comparison is performed on a single value and the flag is set to 1 if the received character equals VAL1.
• If VAL1 is strictly lower than VAL2, then any value between VAL1 and VAL2 sets the CMP flag.
• If VAL1 is strictly higher than VAL2, then the flag CMP is set to 1 if any received character equals VAL1 or VAL2.

When the FLEX_US_CMPR.CMPMODE bit is set to FLAG_ONLY (value 0), all received data are loaded in FLEX_US_RHR and the CMP flag provides the status of the comparison result.

By programming the START_CONDITION.CMPMODE bit (value 1), the comparison function result triggers the start of the loading of FLEX_US_RHR (see the following figure). The trigger condition exists as soon as the received character value matches the condition defined by the programming of VAL1, VAL2 and CMPPAR in FLEX_US_CMPR. The comparison trigger event is restarted by writing a 1 to the FLEX_US_CR.REQCLR bit.

By setting the CMPMODE bit to FILTER (value 2), the comparison result triggers the start of the US_RHR loading. The trigger condition exists as soon as the received address byte value matches the conditions defined by VAL1, VAL2 in US_CMPR. The comparison trigger event is restarted automatically after the reception of the data byte. This comparison mode is only available when FLEX_US_MR.USART_MODE is set).

The value programmed in the VAL1 and VAL2 fields must not exceed the maximum value of the received character (see CHRL field in FLEX_US_MR).