Re: Interfacing to an existing RS-485 Bus
- From: Paul Keinanen <keinanen@xxxxxx>
- Date: Tue, 01 May 2007 09:39:46 +0300
On Mon, 30 Apr 2007 16:45:28 -0500, "schadha" <sanjay@xxxxxxxxxxxxx>
wrote:
We are creating a device which is to be slave device on a RS-485 bus.
I1 I2 I3 I4 > IDLE bytes from the Master
F6 > from Salve to request bus
The problem:
============
On the analyzer we find that I1 and F6 start at the same time.
On the RS-485 half duplex bus this is simply impossible. Use a decent
serial line analyzer with proper time stamps or use a dual channel
oscilloscope.
If these master and slave signals were obtained prior to the RS-485
buffers and they really occur simultaneously (verified by an
oscilloscope), then this is some kind of CAN (Controller Area Network)
style arbitration, which can be implemented also on RS-485 hardware
(in fact the first CAN systems used RS-485 hardware before dedicated
CAN hardware became available).
Paul
.
- References:
- Interfacing to an existing RS-485 Bus
- From: schadha
- Interfacing to an existing RS-485 Bus
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