SLAZ100AA October 2012 – May 2021 CC430F6127
USCI Module
Functional
USCI I2C IFGs UCSTTIFG, UCSTPIFG, UCNACKIFG
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.
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