UART TTL to RS485

I'm not sure I understand the question.  The R and D pins on any RS-485 transceiver operate at TTL levels, so it sounds like you only need to choose a suitable RS-485 transceiver based on your datarate, operating voltage/logic levels, etc.

Let me know if I have misunderstood the functionality you have asked about -- 

Thank you for your answer. I try to clear it up.

I used BlueGiga WT12 bluetooth module with MAX3485 at my first try. Later we have tried several manufacturer’s transceivers but none of them worked.

As you mentioned R and D pins are obvious.

RXD to RO and TXD to DI

The problems are starting here. Which pins will control the data flow? I thought NCTS and NRTS but it not worked for me.

I tried ICs with auto flow control also without success.

RS-232 transceivers are working perfectly.

I hope I was able to explane it in details. I'm a chemical engineer so it's not acually my field of expertice.

Regards.

Krisztián Stoller

Thanks.  I have a few more questions - 

Can you provide a diagram showing exactly how the WT12, 485 transceiver, and your sensor are connected during your test?

What do you mean when you say "none of the 485 transceivers worked"?  Were they not receiving data from the bus?  Not transmitting data to the bus?  It seems like all of the transceivers were probably working, but rather your control scheme was not enabling and disabling the driver and receiver at the appropriate times.

Does your sensor send data via RS485, receive data via RS485, or both?  If it only sends data, you may connect D, DE and /RE to ground, and make the transceiver always a receiver.

Hi!

I will try to get the diagram from our electrical Engineer tomorrow (since it almost midnight here) and add it to this reply.

 

Yes the problem was the flow control. I need communication both ways. My sensors are using MODBUS.

But we never reached an actual test with probes. For testing we set up two computers. 1st was connected to the WT12 module on BlueTooth and the 2nd was connected on an RS-485 serial port. We were able to set the transceiver manually as a receiver and a sender so we are sure the signal conversion would work fine.

But we don't know how to control the flow automatically used by the WT12 (or other BT modules) UART pins. Or I would be fine with an IC with auto flow control also.

Regards.

Krisztián

Hi Eric,

Here is a TI design for an RS-485 to RS-232 converter. There are schematics, layout files, and a design guide to assist you in your design. Please let me know if you have any questions while going through this process.

HI Michael

I stepped in the interface lab, but I can not find the design fold for an RS-485 to RS-232 converter, could you pls give dedicate web link.

Or, can I give you a call.

Best regards
Eric.z

Hi Eric,

Sorry, I never included the link: