SLAZ333AC October   2012  – September 2021 MSP430F6635

 

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6.54 USCI39

USCI Module

Category

Functional

Function

USCI I2C IFGs UCSTTIFG, UCSTPIFG, UCNACKIFG

Description

Unpredictable code execution can occur if one of the hardware-clear-able IFGs UCSTTIFG, UCSTPIFG or UCNACKIFG is set while the global interrupt enable is set by software (GIE=1). This erratum is triggered if ALL of the following events occur in following order:

1. Pending Interrupt: One of the UCxIFG=1 AND UCxIE=1 while GIE=0

2. The GIE is set by software (e.g. EINT)

3. The pending interrupt is cleared by hardware (external I2C event) in a time window of 1 MCLK clock cycle after the "EINT" instruction is executed.

Workaround

Disable the UCSTTIE, UCSTPIE and UCNACKIE before the GIE is set. After GIE is set, the local interrupt enable flags can be set again.

Assembly example:

   bic #UCNACKIE+UCSTPIE+UCSTTIE, UCBxIE ; disable all self-clearing interrupts
   NOP
   EINT
   bis #UCNACKIE+UCSTPIE+UCSTTIE, UCBxIE ; enable all self-clearing interrupts