You might use a low slew rate driver to limit reflections.

Harold

> I concur - you can do everything the wrong way with rs485 and all is
> fine at low bitrates.  If you have a CRC check on your messages, and a
> retry mechanism of some sort (maybe an acknowledgement response and if
> this ack is not seen within a timeout period, a retry), you'll be in
> fine shape.
> J
>
> Mike Harrison wrote:
>> On Sat, 06 Jul 2013 16:42:58 -0400, you wrote:
>>
>>> I will be building a small network of 4 clients to send one of the
>>> house's 4 heating/cooling zones temperature and humidity to a
>>> central processor. The client likely will be 18F1320, and the
>>> processor 18F4320 since I have a few laying around, but could
>>> consider something different. The client will also have a LCD
>>> display. The processor will based on temperature and humidity sent
>>> the house HVAC zone controller and humidifier signals (24VAC) via
>>> relays based on current set conditions.
>>>
>>> The 4 zone lengths from the processor range from 10 to 50 feet and
>>> planning to use cat-5 cable. 2 pair for power to the client, and
>>> one pair for RS-485 signal. The network speed can be very slow,
>>> even down to 300 baud, since 1 message from each client in 1second
>>> and a message length of maybe 20 characters at most would be a
>>> lot.
>>>
>>> The question is: Will a star arrangement work, and what should the
>>> terminating resistors be?
>>
>> That will work fine up to a good few kbaud, no need for terminators
>> at that distance
>>
>>
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