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Designing Bus Transceiver

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SPDCHK

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I designed a Master/Slave serial communications control system using a co-ex cable as the network medium.

It all works 100% over short distances, and to be quite truthful, I haven’t yet tested if for long distances (40-50m). I was planning on using the 74LS243 Bus Transceiver IC, but I don’t have any in stock to test with.

Question: How do I create the same functionality as the Bus Transceiver IC using just discrete components like transistors, diodes and resistors?
As a hobbyist my design sucks to say the least.

Can any of you smart Electronic Engineers perhaps model something for me on LTSpice? (Operating voltage 5V)

Thanks.
 

Wp100

Well-Known Member
Hi,

2 wire serial comms - means RS232 to me - 5v chips like the Max232 range are cheap and popluar.
 

Papabravo

Well-Known Member
A 74LS243 is a bus tranceiver on a PRINTED CIRCUIT BOARD. It is not a cable driver, 18 inches is about the maximum run for an LSTTL output.

There are any number of simple solutions including the multi-drop RS-485 trnasceiver which can drive twisted pair or coax or any other transmission line you may have in mind.

You might also consider the quasi-differential with respect to a common ground transceiver used on DeviceNet. It is made by Philips, the 82C251, and it can drive 500 meters at 125 kBaud.

The discrete solution consists of something like a class AB push-pull stage that drives the cable both high and low. There are some other alternatives depending on your requirements and budget parameters.
 

SPDCHK

Member
75176b

I’ve done some searching and found the following RS485 Transceiver chip (75176B). The only problem now is that the data sheets shows the use of the RO and DI pins to be connected to a microcontrollers Rx/Tx pins individually.

I’m using the PIC12F675 chip that does not support USART. I wrote my code in such a manner that one Pic pin acts as both Rx and Tx pins.

Question: Has anyone used the 75176B before in a one-wire application? Refer to attached PDF file. Can I go ahead and wire the IC as shown?

Thanks.
 

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