Functional safety requirements for application software

AN4475

12/27

DocID026216 Rev 1

requirements as described in the Preface. 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).

Single write digital output with read-back

Implementation hint: SIU pads are used to perform a single write digital output with read-

back. The read-back is done using the external configuration or the internal. SIU pads are

configured as follows (see also Figure 1):

•

External read-back: one SIU pad is configured to allow read-back of the output write on

the selected SIU pad and the loop-back is done with an external connection outside the

device. Using this configuration, external pins are used. In case of External read-back,

the two selected pads are not be physically adjacent;

•

on the selected SIU pad via an internal read path. Using this configuration, a single

external pin is used.

Double Write Digital Outputs

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

are correctly configured and the output write of the selected channels are implemented

following these guidelines:

•

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

•

The two selected pads are 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 is properly configured before writing the PGPDOx

register.

2.9.4

Write PWM outputs

Suggested: [covers: SW_WRT_PWM_OUTPUT] some PWM outputs are 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. [end]

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.

d.

This is not strictly requested. The SPC563Mxx can demand to an external device to check the integrity of the

PWM generation.