AN3077 Datasheet, PDF (19/82 Pages) STMicroelectronics – Safety application guide

AN3077
Functional safety requirements for application software
3.13.1.1 Double Read Digital Inputs
3.13.1.1.1
Hardware elements
Double read operation of a digital input is implemented by two general purpose inputs (GPI)
of the SIUL unit. SIUL must be configured to allow an input signal to be read from it’s
assigned pad. To minimize CCFs, the two input pads must not be physically adjacent (see
Section 7, I/O pin/ball configuration for details).
3.13.1.1.2 Safety Integrity Functions
Mandatory: Safety integrity is achieved by replicated reading and software comparison by
the processing function. The application shall implement the following tests:
● SIUL_SWTEST_REGCRC
Note:
Rationale: To verify that the configuration of the two pads used corresponds with the
expected configuration, and to avoid a CCF caused by incorrectly configured pads
● GPI_SWTEST_CMP
Note:
Rationale: To verify that the two input values compare
Figure 1. Double Read Digital Input
Digital In Double
Read Configuration
SIUL
I ^{= Input Pad}
I
I
GPI[x] GPI[y]
3.13.1.1.3
Software test implementation
● SIUL_SWTEST_REGCRC
The SIUL configuration registers are read, then a CRC is calculated. The CRC
calculation is compared to the expected CRC value.
DocID16384 Rev 10
19/82
81