[SOLVED] Bias & termination resistors in RS485

[vbdev]

I am using one way communication for sending data to display from microcontroller. In this case as the output of 75176 is always enabled, are the bias resistors necessary?

Secondly, the cable length will no exceed more than 5mtrs, so are the termination resistors necessary?

Let me explain my project. It consists of two devices one controller & another is display. Both are having the same microcontrollers (89S52). The distance between them is max 5mtr or slightly more. The controller mcu will send data to the display serially. Due to the need of external capacitors I avoided using MAX232 at both sides.

Then I was not so sure about directly using the mcu UART pins, so I decided to convert it to RS485 level. Am I on the right path? Thanks!

 

[FvM]

Obviously no need for bias resistors. Termination is not absolutely necessary for 5 m cable and usual UART baud rates (e.g. < 920k). Consider that the round trip delay for reflected signals is about 50 ns. Reflections will decay fast enough not to cause transmission errors.

 

[vbdev]

Thanks, now I realized that due to some reasons, I cannot enable the transmitter continuously. So I will use the bias resistors.