MAX1485CUB+,MAX1484EUB+ communication issue - Page 1
Forum section: electronics / projects

author: Ravi Kumar S
author_rank: Newbie
timestamp: October 23, 2024, 08:14:15 am
content: Hello All,We are using MAX1485CUB+ in one of our design product. In this IC, we are facing communication issues.issue:In half duplex mode, the transmitted data from MCU is receiving back to the MCU, which is creating overlap in the data. when data is sent from slave device. For example, if I send (AA BB CC from MCU it will be received in slave correctly, but if the slave is also responding with 11 22 33 in MCU, I'll get 11 AA 22 BB CC 33) We thought this may be because in this IC there is no RE (receive enable) pin.So we ordered MAX1484EUB+ in this IC only one way communication is working. For example, from MCU to slave, if it works, then from slave to MCU we need to swap the A-B wire to get data.With respect to datasheet we are configuring the IC pins but its not working as intended.I have attached the schematic. please help me to resolve this.-Ravi Kumar S

author: PGPG
author_rank: Frequent Contributor
timestamp: October 23, 2024, 10:28:35 pm
content: Quote from: Ravi Kumar S on October 23, 2024, 08:14:15 amIt looks that you don't want to use half duplex so why you are using it?Quote from: Ravi Kumar S on October 23, 2024, 08:14:15 amIt is not clear what you need to swap.As communication in one direction uses its own 2 wires and communication in other direction uses its own 2 wires than swapping one wire pair should have only influence on one direction and from what you write it looks that you have to swap between sending and receiving.If you communicate with some other equipment have in mind that there is no consensus in industry which wire is A and which is B.I have read that the original RS485 marking was opposite to what IC manufacturers use in datasheets, but all IC manufacturers use the same convention.

author: Salitronic
author_rank: Contributor
timestamp: October 23, 2024, 10:45:37 pm
content: Quote from: Ravi Kumar S on October 23, 2024, 08:14:15 amThis is expected with the MAX1485, in half-duplex mode the receiver is always enabled.

author: Ravi Kumar S
author_rank: Newbie
timestamp: October 24, 2024, 10:43:12 am
content: Hi PGPGFor my slave device i need half duplex.wire swappingIn half duplex there is only 2 wire right so let say we are communicationfrom master to slave : AB is connected to AB :in this case i'll get right data in slave(if i send AA from master i'll get AA) and if i send response from slave to master( if i send BB i'll get some garbage data).from master to slave : AB is connected to BA :in this can i'll get garbage data in slave from master and if i send response from slave to mster(same BB i'll send) i'll get BB in master.

author: PGPG
author_rank: Frequent Contributor
timestamp: October 24, 2024, 11:43:44 am
content: Quote from: Ravi Kumar S on October 24, 2024, 10:43:12 amSo the problem is when you are using only A,B lines.My first step in searching a source of problem would be to disconnect Y,Z lines to be sure that what is transmitted certainly is not using these wires.Next is to look with digital scope at signal on its way (before transceiver, at lines A,B, after receiver) and then at its way back to find the place where it is reversed versus what is expected. When you find the place where the problem arises it should be easier to find its source.I think it would be better to replace AA with for example 02 to easier recognize at waveform start bit, data bits and stop bit.