SN65HVD75: low pin count control with DE/RE# and R/D shorted together

Andrea Pastega

Part Number: SN65HVD75

Hello,

I would try a pin reduced approach to sharing a signal for DE/RE# and another for D/R.

Provided that controller will have to change direction of port for D/R signal with proper timing avoiding contention with R, could it be a problem for the transceiver itself?

Thanks

Andrea

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 295240 points

DE and /RE have opposite polarity to allow such sharing.

When /RE is high, R is Hi-Z (see table 2), so it is possible to share D and R. (D has an pull-up resistor, so it is allowed to make the D signal Hi-Z before disabling DE.)

0 Andrea Pastega over 2 years ago in reply to Clemens Ladisch

Prodigy 120 points

Clemens,

thanks for your answer.

From a static point of view I'm sure it will work. I have some concern about the dynamic behavior, i.e. during direction switches. I see in some other posts that somebody experienced unexpected glitches on receiver during TX turnoff.

Provided that shared D/R will be pulled-up, do you expect some erratic behavior during direction switches?

Thanks

Andrea

+1 Clemens Ladisch over 2 years ago in reply to Andrea Pastega

Guru 295240 points

Assuming that you are using a UART(-like) protocol where the idle state is high, and that you switch directions only when idle, there should be no problem.

0 Andrea Pastega over 2 years ago in reply to Clemens Ladisch

Prodigy 120 points

Thanks

0 Parker Dodson over 2 years ago in reply to Andrea Pastega

TI__Mastermind 48257 points

Hi Andrea,

Clemens is correct - as long as the enables are being switched during an idle period there shouldn't be much concern (as mode switches could be a bit longer so doing a switching during an idle period - especially in a UART like protocol should be fine.)

Please let me know if you have any other questions!

Best,

Parker Dodson

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SN65HVD75: low pin count control with DE/RE# and R/D shorted together