AN3077 datasheet(25/82 Pages) STMICROELECTRONICS

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AN3077

Functional safety requirements for application software

3.13.3.1.4

Implementation details

The following hardware elements shall be used for the safety function:

●

eTimer_0 channels

●

eTimer_1 channels

●

External interrupt via GPIO pins (configured via the SIUL)

The user must select one channel from eTimer_0 and one from eTimer_1. The external

interrupt pins are optional.

Mandatory: The pads shall be configured via the appropriate pad configuration registers

(SIUL_PCRn).

Note:

Rationale: To configure pads used by this safety function

3.13.4

Write Digital Outputs

For ASIL D applications, digital outputs used for safety purposes are assumed to be written

either redundantly or with read back as described in the following section.

Note:

Application-dependent option: If a sufficient diagnostic coverage can be reached by a

plausibility check on a single output channel for a specific application, a plausibility check

can replace a redundant write or a direct read back.

The element safety function Write Digital Out is implemented as either:

●

Single Write Digital Out With Read Back

●

Double Write Digital Out

3.13.4.1

Single Write Digital Outputs With Read Back

The SIUL hardware element is used to perform a single Write Digital Output With Read

Back.

Mandatory: The read back must be implemented in one of the two modes shown in

Figure 4.

Note:

Rationale: To verify if written data compares with the expected data

Mandatory: The SIUL element must be correctly configured to provide the output write and

the pad directions as follows:

●

External read back – SIUL is configured to read back the signal from an additional pad,

and the loopback is performed outside the device. In this configuration, only half of the

available digital outputs are available as safety outputs.

●

Internal read back(e) – SIUL is configured to read back the pad value via an internal

read path. All pads dedicated to digital input/output are capable of reading the pad

digital status using the input logic.

Table 5. Software BIST and/or test

Software BIST or test

Frequency

ETIMER0_SWTEST_REGCRC

Once after programming

ETIMER1_SWTEST_REGCRC

Once after programming

SIUL_SWTEST_REGCRC

Once after programming

ENCI_SWTEST_CMP

Once for every acquisition

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