The CMOS levels of the PIC are not suitable for the RS-485 bus. The slew
rate of the PIC is not important because the OP will use a level shifter
between the PIC and the bus.
Some RS-485 level shifters (MAX3079 is one if I remember it right) have
selectable slew-rate.


Best regards,

Isaac


Em 07/07/2013 07:59, Jan-Erik Soderholm escreveu:
> Hi.
>
> I think some PICs has serial ports where the slew rate
> is programmable... (?). Or at least has a "slow" setting
> that can be programmed on or off.
>
> Jan-Erik.
>
>
>
> Carl Denk wrote 2013-07-07 12:18:
>> Thanks for all the replies, and yes I normally have some error checking
>> and retry.
>> Probably will try 1200 baud to start.
>>
>> You might use a low slew rate driver to limit reflections.
>> Can someone suggest an appropriate driver?
>>
>>
>> On 7/6/13 10:08 PM, Jesse Lackey wrote:
>>> 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
>>>

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