SLAZ374AH October   2012  – August 2021 MSP430FR5721

 

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6.39 USCI44

USCI Module

Category

Functional

Function

Differing clock sources may cause UART communication failure

Description

When using the USCI_A UART module with differing clock sources for the system clock (MCLK) and the UART source clock (BRCLK), any read or write of the UCAxIFG, UCAxCTLW0, UCAxSTATW, UCAxRXBUF, UCAxTXBUF, UCAxABCTL  & UCAxIV registers, while the UCATXIFG or UCARXIFG flag is being set by a UART event could unintentionally clear the UCATXIFG or UCARXIFG. This may result in the UART communication being stalled.

Workaround

Workaround 1: Use synchronous clocks to source BRCLK and MCLK. Note that the clock frequencies need not be identical and dividers may be used as long as they are using the same clock source.

Workaround 2: Avoid polling UCAxTXIFG and UCAxRXIFG. Using the standard interrupt service routine to service the interrupt flag significantly reduces access to the USCI registers & hence reduces the probability of this errata occurring.
Also, limit all accesses of the UCAxCTLW0, UCAxSTATW, UCAxRXBUF, UCAxTXBUF, UCAxABCTL, UCAxIFG, & UCAxIV registers while transmit or receive operation is ongoing (and UCAxRXIFG or UCAxTXIFG is expected to be set) as this can further reduce the probability of this errata occurring.