SLAZ453Z May   2014  – August 2021 MSP430FR5849

 

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6.44 USCI47

USCI Module

Category

Functional

Function

eUSCI SPI slave with clock phase UCCKPH = 1

Description

The eUSCI SPI operates incorrectly under the following conditions:

1. The eUSCI_A or eUSCI_B module is configured as a SPI slave with clock phase mode UCCKPH = 1

AND

2. The SPI clock pin is not at the appropriate idle level (low for UCCKPL = 0, high for UCCKPL = 1) when the UCSWRST bit in the UCxxCTLW0 register is cleared.

If both of the above conditions are satisfied, then the following will occur:
eUSCI_A: the SPI will not be able to receive a byte (UCAxRXBUF will not be filled and UCRXIFG will not be set) and SPI slave output data will be wrong (first bit will be missed and data will be shifted).
eUSCI_B: the SPI receives data correctly but the SPI slave output data will be wrong (first byte will be duplicated or replaced by second byte).

Workaround

Use clock phase mode UCCKPH = 0 for MSP SPI slave if allowed by the application.

OR

The SPI master must set the clock pin at the appropriate idle level (low for UCCKPL = 0, high for UCCKPL = 1) before SPI slave is reset (UCSWRST bit is cleared).

OR

For eUSCI_A: to detect communication failure condition where UCRXIFG is not set, check both UCRXIFG and UCTXIFG. If UCTXIFG is set twice but UCRXIFG is not set, reset the MSP SPI slave by setting and then clearing the UCSWRST bit, and inform the SPI master to resend the data.