Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!stout!cook From: cook@stout.ucar.edu (Forrest Cook) Newsgroups: sci.electronics Subject: Re: Using MC1488 for TTL->RS-232 Message-ID: <5923@ncar.ucar.edu> Date: 8 Jan 90 01:56:52 GMT References: Sender: news@ncar.ucar.edu Reply-To: cook@stout.UCAR.EDU (Forrest Cook) Organization: Field Observing Facility, NCAR, Boulder, CO Lines: 24 In article kg19+@andrew.cmu.edu (Kurt A. Geisel) writes: >I am trying to convert a TTL signal into an RS-232 signal. ... >When the TTL input is at 0 V, the RS-232 output is at 3.25 V. When >the TTL input is at +5 V, the RS-232 output is at 3.94 V. Needless to >say, this is useless. I would recommend supplying the 1488 with +/- 10 Volts minimum, +/- 12 is better. RS-232 with output swings less than +/- 7 Volts will have problems driving all manufacturer's receiver chips at high baud rates over longish lines. The spec says the length should be < 50 feet, I'm not sure what kind of wire and max baud rates are within spec. I am guessing that your system only has 5V supplies, and putting in a +/- 12 V supply is kind of expensive for just a little RS-232 driver. Maxim and Intersil (and others?) make some really great RS-232 driver/receiver chips that have built in charge pumps so that you can get +/- 10V signals using only a 5V supply. The original chips from Maxim had some problems, but I have had no problems with recent batches. ^ ^ Forrest Cook - Beware of programmers who carry screwdrivers - LB /|\ /|\ cook@stout.ucar.edu (The preceeding was all my OPINION) /|\ /|\ {husc6|rutgers|ames|gatech}!ncar!stout!cook /|\ /|\ {uunet|ucbvax|allegra|cbosgd}!nbires!ncar!stout!cook