Urgent help needed:RS232 to RS485 converter

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czar

Joined: 16 Feb 2008
Posts: 4

02 Jul 2008 10:05 Urgent help needed:RS232 to RS485 converter

hi
I am using a device which communicates thru rs485 half-duplex interface.The required baud rate is 19200 bps.Presently i am using the circuit (i have attached it) which uses max 232 and max 485 to do the conversion.Actually i'm in a bit of a hurry and have to do this thing in 2 days max.Also i will not be able to get any other ics besides these so i'm stuck with max232 and max485.

Some of the problems i'm facing are:
1)the device is sending back the same data i'm transmitting
2)wat software should i use ?
3)wat type of flow control should i use?

thnax a ton for seeing my post.
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Abhishek

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davidgrm

Joined: 08 Apr 2006
Posts: 232
Helped: 21

02 Jul 2008 11:24 Re: Urgent help needed:RS232 to RS485 converter

According to your diagram you should not get transmitted data coming back to you. That happens when the RE line is permantly enabled. Take a look at my comments on this post:
http://www.edaboard.com/viewtopic.php?p=1051545#1051545

czar

Joined: 16 Feb 2008
Posts: 4

02 Jul 2008 12:13 Re: Urgent help needed:RS232 to RS485 converter

actually the protocol which the device uses requires me to send a sequence of 6 bytes and then the device responds.here the rts line needs to be controlled manually, i think that's leading to the lapse of communication.is there some way this flow control can be automatic and fiddling with the rts line could be avoided,if not wat can i do to solve my problem?(Note:i cant alter the protocol of the device)

It would be great if u could also let me know which software and wat flow control(harware/xon xoff/none) should i use?

are there any other circuits (made by max232 and max485) which i can use?

thanx

IanP

Joined: 05 Oct 2004
Posts: 6490
Helped: 1542
Location: West Coast

02 Jul 2008 13:55 Re: Urgent help needed:RS232 to RS485 converter

Take a look at this circuit:
http://www.edaboard.com/viewtopic.php?t=156484
If your RS-232 accepts 0-5V levels it should work without any changes at baud rates of up to 115kbps ..
Rgds,
IanP

DrBob13

Joined: 26 Mar 2008
Posts: 140
Helped: 36
Location: UK

04 Jul 2008 13:32 Re: Urgent help needed:RS232 to RS485 converter

Hi,
If you have it connected it to the RTS line as shown it should work as stated previously, the recieve line should go hiZ if the RTS line is high so there should be no local echo. Do you have a short on your board or is the receiving device on the RS485 echoing back the characters if they are not recognised. Do you get this if nothing is plugged into the RS485? Have you got the A/B lines the correct way round they join to their own letter at all nodes, with RS485 do not cross them like RS232. This might cause a local echo but I am guessing as I have not seen it happen in practice (yet).
Bob