RS485 Baud rate

[abdelkarim]

Hello there, i have designed a board with RS485 communicatin . i have used the MAX485 IC . My problem is that the communication is working very well when the baud rate is 9600 and when i try to increase it to 115200 for exemple it dosen't work ! .
Please any idea to help me ?

[qdrives]

Have you added 120 ohm termination at both ends?
Make sure that the drive enable pin is made low as soon as the last stop bit is transmitted.

[abdelkarim]

yes i added the 120 ohm resistor

[robertferanec]

how long is the cable?

[abdelkarim]

the cable is <1 m

[robertferanec]

do two the same devices (e.g. your board talking to your board) talk to each other or are they different devices (e.g. your board talking to a PC)? the problem could be also inaccurate frequency of UART signal

[abdelkarim]

my board is talking to a pc

[robertferanec]

Did you consider your MCU frequency based on timing accuracy for the UART at 115200?

This is what I mean, here are some examples: https://www.google.com/search?q=mcu+...WGiOLdTofVh-9M