Electronics > Beginners

Bi-directional uart

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piam:
Hi,
I have a circuit that I'm trying to implement that is quite old and uses RS232 to communicate bi-directionally over a single pin to an MCU.

Here's the circuit:


I'd rather not use RS232 and just want to communicate using a rasperry Pi or similar with PTA0, but it both receives and transmits over a single pin. Can someone suggest how I might do this natively on a pi, either by driving a GPIO bi-directionally and doing this in software, or using the native UART and somehow tieing rx and tx together, perhaps with some other chip?

Berni:
And why not just connect pins 16 and 15 of that MC145407 to the RX and TX pins of a raspberry UART port?

piam:
I don't have the MC145407 or MC74HC125 and was hoping to avoid it if I didn't need them.

Berni:
In that case why not just buy a off the shelf USB to RS232 dongle and use it with a DB9 do DB25 serial adapter.

mvs:

--- Quote from: piam on January 09, 2020, 11:28:11 am ---I don't have the MC145407 or MC74HC125 and was hoping to avoid it if I didn't need them.

--- End quote ---
You do not need RS232 driver (MC145407), but perhaps 3.3v <-> 5v level shifter (RPi has 3.3v IO levels).

74hc125 is just cheap Tri-state buffer. You may replace it with a small signal diode (cathode to RPi TX, anode to RPi RX and PTA0 + Pullup R).

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