BIST ON LINE TEST and MC33908

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BIST ON LINE TEST and MC33908

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mauriziogreco
Contributor III

Hi , all.

I have this doubt.

The BIST works with a internal reset at the end of the test.

In our project we are using the approach described by NXP for MC33908.

SBC.png

Having the reset, the FCCU_0, FCCU_1 will be drived by external pull-up, pull-down resistor into Error condition for SBC. The SBC will produce a reset (external reset) for the MCU. The result is that we loose possibility to read result of BIST ON LINE test.

SBC_2.png

How is possible solve this issue?

Is a solution try to perform BIST without scheduling final reset?

It's a solution do not use the pull up on FCCU_1 (use a pull down) and do not use a pull down on FCCU_0 (use a pull up) ?bi-stable protocol.png

Thanks into advance, for all answer.

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petervlna
NXP Employee
NXP Employee

Hi,

The reset on ONline BIST complete is necessary.

You will analyze the data after reset. STCU will hold online BIST results trough BIST reset.

It is not necessary for SBC reset to be involved as the reset is triggered by micro itself.

And it is not clear which MPC57xx device you are using. They are not the same.

Peter

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mauriziogreco
Contributor III

Hi , Peter.

You're right! I forgot MCU. We are working with 5777C.

The problem is:

a) at the end of BIST, MCU 5777C restart itself

b) during the re-init of MCU (some ms) the port of EOUT of FCCU are into "high impedance" as input (and only some ms they will be driven as GPIO or as ALTERNATE 3 function for FCCU EOUT port) so Eout0 is low and Eout1 is high (error condition) fixed by pull resistor (coming from SBC safety manual reference notes)

c) we are using SBC MC33908, initialized to react on EOUT activity

d) during the auto-reset of MCU, the MC33908 is not restarted, so it's continue to monitor EOUT  activity

e) MC33908 cannot change its configuration about reaction on EOUT  activity (once written value of some register cannot be changed)

f) during re-init of MCU, the Eout ports are driven to communicate Fault condition (bi-stable protocol) because there are present pull resistor suggested by Safety Manual of SBC

The only solution I found is  remove the pull resistor suggested by Safety Manaul of SBC (reported in my question as print-screen) and fix pull resistor in following way:

Eout0 connected to pull-up 5V

Eout1 connected to pull-down 0V

But .... I m not sure this is good solution.

Have you other ideas?

Thanks

Maurizio

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