Newsgroups: comp.robotics
Subject: Long Serial I/O Lines
From: robin.hunziker@mecheng.fullfeed.com (Robin Hunziker)
Path: brunix!cat.cis.Brown.EDU!agate!howland.reston.ans.net!math.ohio-state.edu!uwm.edu!daffy!uwvax!gorgon!fullfeed!mecheng!robin.hunziker
Distribution: world
Message-ID: <af.6041.33.0NAF86BA@mecheng.fullfeed.com>
References: <Donald.Heller.134.0010A506@jpl.nasa.gov>
Date: Sat,  2 Jul 94 12:01:00 -0600
Organization: MechEng / American Society of Mechanical Engineers
Lines: 33

Subject: Long Serial I/O Lines

DH>I would like to establish one-way serial communication between two
  >microcontroller-based unit which will be 500 to 1000 feet apart.
  >This is for a scoreboard for my local Little League.  The local
  >unit will have a keypad (for bumping scores, strikes, etc.) and the
  >remote unit will have drivers for (huge) 7-segment displays and
  >lights.  I hope I can use cheap phone wire, using 3-wire RS232.  I
  >assume I'll need some kind of driver to go the distance, though.
  >I've heard of something called I2C, a two-wire improvement, with
  >available drivers. My plan is to use PICs for the brains.  This is
  >my first project; I have the PICStart kit from a Microchip seminar.

IC started out as an intra-PCB serial link (i.e. similar to SPI).  I
think that it was developed by Philips.  Philips created ACCESS.BUS
which is an enhanced IC and used to multi-drop slow peripherals
(e.g., keyboards) to a computer.  Thus both IC and ACCESS.BUS
probably are not optimum for your application.  However, Circuit
Cellar Ink has covered ACCESS.BUS in some detail (June 1993 at least)
and you may want to check back issues if possible.  The Circuit Cellar
BBS is 203/871-1988 (871-0549 for HST).

I recommend you consider EIA-485.  Where EIA-232 (aka RS232)
officially supports 50' max cable, EIA-485 supports up to 4,000'.
Maxim (800/998-8800) offers a wide variety of chips and free samples.
2 wires are generally used for half-duplex & 4 wires for full duplex.
Many others including Motorola, TI and Linear Technology offer EIA-485
chips.  I don't know about PICs, but MicroSys/Drumlin (818/244-4600)
offers x86 and 8051 comm libraries specifically for EIA-485 and also
ISA (ATbus) boards.
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  QMPro 1.52  Sometimes you're the windshield, sometimes you're the bug

