What is the impact of shorting FS0B to High on the FS26xx while in debug mode ?

[MFaheem]

Hello, 

Short version: What is the impact of shorting FS0B to High on the FS26xx while in debug mode ? 

Long version: to be able to debug S32K344 Target connected to FS26xx Chip, the SBC needs to be in debug mode however you cannot release FS0B while in debug mode, as per the datasheet you need to exit debug mode first then release the safety outputs, What I tried to do is keep the FS26 in debug mode but force the FS0B to high externally via GPIO pin from S32k344, SBC is no longer communicating on SPI but the target is powered on Normally !! any explanations ? 

[guoweisun]

You can see the safety manual that  when short FS0B to High, the RSTB assertion LOW.

[MFaheem]

Yes that would be the expected behavior if not in "debug mode" AND "BACKUP_SAFETY_PATH_FS0B == RSTB assertion" ... however that is not the situation I described ... I'm currently having almost dead SBC when testing the short to high scenario on FS0B, SBC is no longer communication on SPI

[guoweisun]

When SBC RSTB assert LOW, does you MCU side work normally?

[MFaheem]

the RSTB line doesn't go low if I'm in debug mode (when FS0B short to high), isn't it ? ... this only happen in normal mode !

[guoweisun]

In datasheet page222 DEBUG mode flow picture, which step do you short the FS0B to high?

[MFaheem]

Before Exiting Debug mode as shown in the pic, and intentionally don't exit debug mode afterwards, I want to keep the SBC in debug mood, but I still want to be able to communicate with it.

[guoweisun · Accepted solution]

FS26 Datasheet shows:

1. RSTB Reaction is decided by BACKUP_SAFETY_PATH_FS0B when FS0B short to high.

2. BACKUP_SAFETY_PATH_FS0B is RSTB Asserted by defualt.

So RSTB is low by default in FS26 if FS0B short to high and customer did not configure it. SPI will not have response when RSTB is low.

[MFaheem]

Well, in my situation BACKUP_SAFETY_PATH_FS0B is left with default setting which is assert the RSTB, however I that the FS0B short to high is either not monitored or no action will be taken if SBC in Debug mode, cuz im still able to debug the target while having the FS0B short to high ... for the SPI communication in this scenario, I managed to get it working and the problem i had was due to some misconfiguration in PORT module