Functional safety requirements for application software

AN4287

12/27

DocID024464

Rev 2

safety outputs. In case of External read-back, the two selected pads shall not be

physically adjacent;

•

on the selected SIU pad via an internal read path. Using this configuration, all available

digital outputs can be used as safety outputs.

Double Write Digital Outputs

Implementation hint: SIU pads are used to perform a double write digital output. SIU pads

shall be correctly configured and the output write of the selected channels shall be

implemented following these guidelines:

•

The two outputs are written with a single instruction to the appropriate register;

•

The output register is read-back.

The two selected pads shall not be physically adjacent to minimize CCFs. Each pad not

dedicated to a specific function can be configured as GPIO with the exception of ADC pads,

as they can only be configured as GPIs. SIU pads can be configured via the relevant pad

configuration registers (PCRn).To write two (or more) GPIOs with a single write instruction,

the Parallel GPIO Pad Data Out (PGPDOx) register can be used. User has to take care that

the two selected GPIOs are controlled by the same PGPDOx register. To protect the value

of the other GPIOs that belong to the same PGPDOx register, the Masked Parallel GPIO

Pad Data Out (MPGPDOx) register shall be properly configured before writing the PGPDOx

register.

3.9.4

Write PWM outputs

Suggested: some PWM outputs shall be written either redundantly or with read-back. Write

PWM output operation can be implemented as single write PWM output with read-back or

double write PWM output.

Rationale: to verify that the two sets of data match.

c.

Internal read back does not cover package faults (e.g. wire bond). Refer to the specific reference manual to

verify the availability of the internal read path.