More and more sounds like a job for an FPGA. The logic flow appears
simple enough and I/O availability wouldn't be a problem. There's an
investment in hardware and a learning curve, however.
Tony
-----Original Message-----
To: Multiple recipients of list CHIPDIR-L <[email protected]>
Sent: Tue, 23 Aug 2005 09:04:22 -0800
Hi,
It's a calibration system, and as such it requires high reliability.
Networking and addressing leaves the system open to problems such as
if one RS485 chip goes short circuit, for example, it will bring the
whole
network down and screw up the (lengthy) calibration process
Therefore IT MUST be designed this way, unless you can think of
anything
better
Separating each channel isolates unit specific problems to just that
channel
-----Original Message-----
Declan Moriarty
Sent: 23 August 2005 17:49
To: Multiple recipients of list CHIPDIR-L
Recently, Somebody Somewhere wrote these words
Hi,
Thanks.
I think I should have been more specific.
We've got an RS485 comms pair, which we want to multiplex between 120
RS485 pairs.
I.e. 120 channels to 1 (or 240 to 2 in terms of actual wires).
Ive seen a 32 channel analogue switch from Analogue devices, but im
unsure as to whether an Analogue switch will be ok?
To quote the Irishman who was asked for directions to somewhere:
"You know... If I was you, I wouldn't start from here at all!"
You are never going to stand up 1-->120 in an RS485 link without such
heartache as to justify a sane design. What's your baud rate? You would
also need sample & holds everywhere. Network the things and address
them. Start over, my friend.
Imagine when you get the complaint "Channel 87 goes intermittent after
about 5 minutes" How will you sort that?
BTW, the trick with analogue switches is never bring the input below the
negative rail.
--
With best Regards,
Declan Moriarty.
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