AN3077 datasheet(19/82 Pages) STMICROELECTRONICS

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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

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.

SIUL

Digital In Double

Read Configuration

GPI[y]

GPI[x]

= Input Pad

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