TMS570LS3137 : Usused Pins FRAYTX1, FRAYTXEN, FRAYTX2, FRAYTXEN2 with no default Pull State

Mike Coombes

Other Parts Discussed in Thread: TMS570LS3137

Hi, On the TMS570LS3137

The data for pins FRAYTX1, FRAYTXEN, FRAYTX2, FRAYTXEN2 is Output with no default Pull State. (Page 24 SPNS162B)

and based on the NOTE (Page 10 SPNS162B) regarding pin state in RESET

When nPORRST is low... All output-only signals are configured as inputs while nPORRST is low, and are configured as outputs immediately after nPORRST goes High.

So whilst nPORRST is low, the state of FRAYTX1, FRAYTXEN, FRAYTX2, FRAYTXEN2 is non deterministic, however deterministic once nPORRST goes high.

Good practice is to pull non deterministic pins to a known state. However I don't really want to comprise my tracking by adding 4 resistors on my PCB, if they are not needed.

Could these line floating in RESET cause latch up, unexpected behaviour, or damage of the TMS570?

Many Thanks, Mike [UK]

over 10 years ago

0 Sunil Oak over 10 years ago

TI__Mastermind 49120 points

Hi Mike,

I will check on this and get back to you.

Best regards,

Sunil

0 Mike Coombes over 10 years ago in reply to Sunil Oak

Prodigy 150 points

Thanks Sunil,

Also I notice RTCK seems to be non deterministic during RESET. perhaps you could check that too. - Mike

0 Sunil Oak over 10 years ago in reply to Mike Coombes

TI__Mastermind 49120 points

Mike,

RTCK as well as the FlexRay TX and TXEN signals are different from other peripheral functions in that they only have output buffers driving the terminals. These outputs are gated off when nPORRST is low, which essentially means that they are tri-stated (or floating).

We will add a recommendation in our datasheets to pull these terminals externally to prevent them from floating when nPORRST is asserted.

Regards,
Sunil

0 Mike Coombes over 10 years ago in reply to Sunil Oak

Prodigy 150 points

Thanks, Great info fast...

In my design I am not using FlexRay, so I am not concerned about floating output as you described above.
As I see it... a Floating output is only a problem if connected to an input without PU / PD.

Correct me if my thoughts on this are wrong.

_mike

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TMS570LS3137 : Usused Pins FRAYTX1, FRAYTXEN, FRAYTX2, FRAYTXEN2 with no default Pull State