[SOLVED] Replacemant of RS232 with RS485

[shahbaz.ele]

dear all
I have a code in FPGA that transmits data via RS232.
Now I have to send this data at 1Km distance. I think RS485 will do this job.
My question is that will my code for RS232 work for RS485, and second what are the changes I should made at receiver end where I am using a PC.
Thanks to all members in advance.

 

[Venkadesh_M]

Hi RS232 is full duplex and 485 is half duplex so you may need two channel of 485s so totally 4 wires for communication and at the PC node, you need to convert the RS232 485 standard...

A half duplex connection could be,
**broken link removed**

 

[debabrta kar]

yes your rs232 code will work for rs485 ..but u just need to take care of the control pin for swtching between transmission and reception.....(RE AND DE PIN)...

 

[betwixt]

I would argue it wouldn't work unless the FPGA handled TX/RX switching. How complicated that is will depend on the application and existing FPGA contents. RS232 (which I doubt the FPGA itself produces) is a three wire system, ground TX and RX whereas RS485 uses ground and shared TX/RX wires. If you have enough wires in the cable, at least one ground and two twisted pairs, I would suggest replacing the existing RS232 interface with RS422 or RS432 instead. These should handle 1Km easily. You can convert FPGA->RS232->RS4x2 but the extra circuitry only adds to cost and possibly limits the top speed, skipping the RS232 stage altogether is best.

Brian.

 

[FvM]

Reading the question literally, this is an unidirectional data transmission which could use an always enabled transmitter. No special requirements except drivers.

 

[betwixt]

If FvM's message is correct, it makes little difference which driver is used as they all work on the same differential low voltage system. All you would need is another differential receiver at the 'far' end to convert back to the FPGA logic levels. Over 1Km you would almost certainly need a terminating resistor acros the wires at the receiving end.

Brian.

 

[shahbaz.ele]

dear all
thanks for reply.
FvM is right I need only ONE direction data transmission (from FPGA to PC).
Rx/Tx line could be hard connected (5V or 0V).
In these conditions can I use Venkadesh_M's circuit.

- - - Updated - - -

dear Venkadesh_M
is it
1. RS485 to RS 232 or
2. RS232 to RS 485
I need
second one.