In SX Microcontrollers, SX/B Compiler and SX-Key Tool, kjennejohn wrote:

RS-422 (push-pull) and RS-485 (RS-422 with multi-drop networking) are the way to go if you have already gone to the expense of installing RS-4xx on your PC. RS232-RS4xx adapters are available from blackbox.com, starting around $110. If there is no PC involved, then so much the better.
I recommend you use the LTC485 or LTC1481. These have superior ESD protection. The LTC485 is available at Digikey.com for $2.50 each, DIP-8, in bulk. The LTC1481 is $2.75 to $3.38.

We use an Intel protocol, called BitBus, AKA IEEE1118. This is RS-485, with a master and over 200 slaves.  Address 0 is the master. Addresses 1 through F(15), and FF(255), are reserved. This leaves you with 239 addresses for slaves. Communications speeds are 64k, 375k, and 1.2meg bits/sec.Even cheap twisted pair, unshielded, will work over a couple hundred feet.
Now: do you want synchronous with that? If yes, you have to supply another RS-4xx circuit to carry the clock. If you have to put repeaters in the loop anywhere, you have to supply yet another circuit to control direction.

'Luck!
kenjj

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