That's sounds quite simple.  I have seen that the 18F EUSARTs can do=20
RS-485, so the transceiver-only option looks quite workable.  I found=20
lots of info on the modbus protocol, but will get to reading it over the=20
weekend.  Thanks.

-Neil.


On 7/31/2012 4:00 AM, Ruben J=F6nsson wrote:
> You just need the transceiver chip - ISL3179 for 3(.3)V logic or MAX487 f=
or 5V
> logic. If it is just inside the oven and you keep the baudrate to, say
> 19200bps, you won't even need termination resistors.
>
> For half duplex (3 wire, rx/tx+, rx/tx- and common) You need the RX and T=
X
> signal from the pic (obviously) and you also need an output to control th=
e
> direction (transmitting or receiving). I think that the USART in some pic=
s even
> can drive the direction signal automatically.
>
> Apart from the direction signal it is just like RS232. And on a pic that =
should
> not be a problem. Also keep in mind that Modbus is quite timing sensitive=
 but
> that should not be a problem on a pic either.
>
> /Ruben
>
>
>> I need to interface a PIC-based circuit to a few devices (PID
>> temperature controllers) via RS485/modbus, and looking for suggestions
>> on a simple way to do this.  This is a one-off project for my reflow
>> oven, so I'm looking for an off-the-shelf interface.
>>
>> Signal-wise, RS-232 to RS-485 is fine, and I can find interfaces from $5
>> to >$100, so not sure what features I should be looking for.  I don't
>> mind getting something on the higher end of that range if I can trust it
>> will be reliable and work properly.  An open (ie: non-enclosed) PCB
>> would be ideal, as I'll add this inside the enclosure with my own
>> circuit board.  TTL-level serial would also be preferred rather than
>> RS-232 level... if that choice exists.
>>
>> Any recommendations?
>>
>> Thanks,
>> -Neil.
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D
> Ruben J=F6nsson
> AB Liros Electronic
> Box 9124, 200 39 Malm=F6, Sweden
> TEL INT +46 40142078
> FAX INT +46 40947388
> ruben@pp.sbbs.se
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D
>

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