Smallest chip for use rs485

[bauche]

Can somebody tell me if is it possible to use rs485 on 12F series like 12F1840...and if i cant use on 12F ....which one is the smallest pic i can use with rs485???

Thanks for your help!!!

[Gabriel]

Its irrelevant.... any pic can handle it. You need a driver IC for the diferential signals which most often will take raw serial as an input.
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CCS PCM 5.078 & CCS PCH 5.093

[Ttelmah]

Take a step back.

RS485, is a signalling standard. No PIC actually generates this....
As Gabriel says, you need a driver IC.

However you then have the question of what protocol you want to use 'over' this standard. There are literally hundreds of protocols that use RS485 signalling. Modbus, Profibus, etc. etc..
Now, some of the protocols can be generated/handled using a 12F chip, but some have large packets, and are relatively complex, which then means that depending on the speed involved, a UART becomes 'necessary', and larger amounts of RAM, and ROM, may be needed, making them hard/impossible to handle in smaller chips. Also, in many cases, there will be restrictions on the timing accuracies, which may well make a crystal or resonator 'necessary'.

The only PIC12's that have a UART, are the , 12F1572, 1822, and 1840.

Then depending on the protocol you intend to use, you have to look at the amounts of ROM/RAM that will be needed. The 1840 chip is easily 'as capable' as many of the PIC16's that have in the past been used to handle a variety of protocols over RS485.

However don't get hooked on 'size'. A 20pin PIC18, in SOIC, will be no larger than an 8pin PIC12 in PDIP, and by the time you add connectors, the driver IC, termination, etc. etc., the size of the chip is the least of your worries. Having more 'grunt'/space in the chip, is likely to make it easier to buffer data, perform arithmetic etc..

Identify the protocol to be used. Work out how much data the chip will need to hold. Try some code (on a larger chip), and see how large it is likely to become, _then_ make your decision on how large the PIC will need to be.

[temtronic]

Have to agree with Mr. T about 'size' !! It's the LAST thing to consider for any project be it one-off or a large production run. It's more than just a PIC on a board, several other components as well as some form of 'connection' to the real world. Too often the 'smaller is better' idea just doesn't work.If 'one-off' YOU have to hand solder those itty bitty parts and on a 'big run' the cost for a board 2x the size is only a penny or two.Heck 4 holes in the corners to mount the PCB can easily take up MORE area than a PIC.
Please step back, rethink the 'size' issue.As Mr. T. says you can get a LOT more features in a slightly bigger PIC and you ALWAYS need another I/O pin,extra RAM or EEPROM.

hth
Jay