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From: email@example.com (john jardine)
Subject: Re: RS485 help #2
Date: 24 Oct 2002 11:42:19 -0700
NNTP-Posting-Date: 24 Oct 2002 18:42:19 GMT
"EBG" wrote in message news:...
> I designated this #2 as I wanted to start fresh with a new post.....thanks
> for all the response on my previous "RS485 termination" post a few days ago.
> Jim, especially.
> Let me ask this.....
> The fact is, I don't care whether my interface really conforms to a specific
> "standard"...RS232 422 or 485.
> My goal is to have a "star network" (central PIC transmitter with branches).
> I neeed to transfer data at a mere 1200 baud (fact is, it can even go lower)
> to up to 10 PIC receivers, which simply do some switching tasks.
> I need however, to eliminate the EMI emmisions coming from the cable by
> using a balanced connection.
> How about this.....
> Has anyone built their own balanced network using a dual optoisolator (say a
> PS2501-2)at the xmtr and each of the receivers? Couldn't this be done? Just
> split the RS232 coming out of the pic, invert one side and drive the
The RS485 type method of sending *is* a digital, differential,
-balanced- system. Both ends can float wrt each other.
If you were using fibre optic cables, then no problem.
If copper wires, then the opto's are going to need a floating power
supply to make them work. We still have RS485 type balanced square
waves travelling the cables so the EMI will be identical. Only
improvement will be that the TX RX ends can float at wider potentials.
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