kg19+@andrew.cmu.edu (Kurt A. Geisel) (12/30/89)
Help a poor non-EE :
I am trying to convert a TTL signal into an RS-232 signal. I was
under the impression that this can be done simply with the MC1488
monolithic quad serial line driver. Here is my set-up:
2 |----------| 3
TTL ---------->| |---------> RS-232
1 | MC 1488 | 14
-5 V --------->| |<--------- +5 V
7 | |
GND ---------->|----------|
What I get:
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.
All the power supply lines have been check and re-checked.
Do I have a bad chip or am I missing some glue?
Any help would be greatly appreciated,
- Kurt
Kurt Geisel SNAIL :
Carnegie Mellon University 65 Lambeth Dr.
ARPA : kg19+@andrew.cmu.edu Pittsburgh, PA 15241
UUCP : uunet!nfsun!kgeisel "We just need to short-circuit the continuum on a
BIX : kgeisel 5 or 6 parsec level." - Forbidden Planethenry@utzoo.uucp (Henry Spencer) (01/01/90)
In article <MZb4w2600WB88M=4wv@andrew.cmu.edu> kg19+@andrew.cmu.edu (Kurt A. Geisel) writes: >I am trying to convert a TTL signal into an RS-232 signal. I was >under the impression that this can be done simply with the MC1488... >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. >Do I have a bad chip or am I missing some glue? I'd say you have a bad chip; I breadboarded the same setup you describe and got +4.5 at 0 and -4.5 at +5, roughly. However, note that you are violating the rules: the MC1488 is specced for 9V or 12V supplies, and is not guaranteed to work properly on 5V. Not only that, even if it does sort of work, as mine did, -4.5 and +4.5 are not RS232-conforming output voltages: -5 and +5 are the minima. The right way to convert TTL to RS232 is to use the Maxim MAX232 or any of several related chips from Maxim and others. They include both transmitters and receivers, generate the necessary voltages themselves from +5 (with the aid of a few capacitors), and hew rather closer to the RS232 specs to boot. The MC1488 is obsolete. -- 1972: Saturn V #15 flight-ready| Henry Spencer at U of Toronto Zoology 1989: birds nesting in engines | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
larry@kitty.UUCP (Larry Lippman) (01/01/90)
In article <MZb4w2600WB88M=4wv@andrew.cmu.edu>, kg19+@andrew.cmu.edu (Kurt A. Geisel) writes: > I am trying to convert a TTL signal into an RS-232 signal. I was > under the impression that this can be done simply with the MC1488 > monolithic quad serial line driver. Here is my set-up: > ... > 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. > All the power supply lines have been check and re-checked. I bet you overlooked something... > Do I have a bad chip or am I missing some glue? The 1488 is typically operated with a Vee of -12 to -15 volts and Vcc of +12 to +15 volts. According to your schematic (which I deleted for brevity), you are using -5 volts for Vee and +5 volts for Vcc. Use the correct voltage range for Vee and Vcc and the chip should work just fine. <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {boulder|decvax|rutgers|watmath}!acsu.buffalo.edu!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {hplabs|utzoo|uunet}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"
freeptos@mips.COM (Dan Freitas) (01/01/90)
>The right way to convert TTL to RS232 is to use the Maxim MAX232 or any >of several related chips from Maxim and others. They include both >transmitters and receivers, generate the necessary voltages themselves >from +5 (with the aid of a few capacitors), and hew rather closer to >the RS232 specs to boot. The MC1488 is obsolete. >-- I just got a sample of such a chip from Motorola. It is the MC145407 5v only driver/receiver. Drives/Receives 3 separate lines. You add (4) 10uf caps, 5v and your on your way. Dan Freitas -- UUCP : {decvax,ucbvax,hplabs}!decwrl!mips!freeptos or freeptos@mips.com USPS : Mips Computer Systems; 930 Arques Ave; Sunnyvale, Ca 94086 PHONE: 408-991-0217
kg19+@andrew.cmu.edu (Kurt A. Geisel) (01/01/90)
Thanks for all the help. The consensus seems to be: it should work, but you really should be using +/- 12v. Well, this is very temporary and very hardware specific, so I think I'll stick with it for now. The port I'm trying to drive seems to accept stuff well under the 232 spec. A MAX232 I'd have to order, while 1488s I can get a Radio Scrap. - Kurt
dnelson@mthvax.cs.miami.edu (Dru Nelson) (01/02/90)
Dan Freitas already posted about this, but if you wanted some more
details, here is an original article by the Motorola rep who posted about
those chips. It has the phone numbers and the other chip.
-------------
Another source for +5 volt only supply voltage RS-232 transmitters
and receivers is
Motorola Semiconductor Products
the original inventor of the MC1488 and MC1489, the "standard"
RS-232 devices used for the last several decades.
The 5 volt only devices from Motorola are the MC145406L or P (ceramic
or plastic package) and the MC145407P. The MC145406 requires + and -
5 volts to + and - 12 volts power supply to meet the full RS-232
spec (withstand input voltages up to + and - 25 volts, etc.). There
are 3 drivers and 3 receivers per package.
Recently introduced is the + 5 volt only MC145407P which only requires
+5 volt input supply and generates internally + and - 10 volts to
permit full compliance with the RS-232 spec. There is enough supply
power generated to power an additional MC145406 device if so desired.
The MC145407 has three drivers and three receivers also.
For additional information, data sheets, etc., contact your local
Motorola Semiconductor sales office, your local Motorola distributor,
or call 1+800-521-6274.
No disclaimer. Obviously Motorola pays me to say all of the above.
~Newsgroups: comp.lsi
--
<< Usual Disclaimer >>
Phil Weinberg @ Motorola Semiconductor, Sunnyvale, CA 94086-5395
UUCP: {hplabs, mot,} !motsj1!phil
Telephone: +1 408-991-7385
---------------
--
%% Dru Nelson %% Miami, FL %% Internet: dnelson@mthvax.cs.miami.edu %%hpoppe@bierstadt.ucar.edu (Herb Poppe) (01/03/90)
Converting TTL to RS232: Maxim MAX232 Motorola MC145407 Question: Are either/both of these parts CMOS? Herb Poppe NCAR INTERNET: hpoppe@ncar.ucar.edu (303) 497-1296 P.O. Box 3000 CSNET: hpoppe@ncar.CSNET Boulder, CO 80307 UUCP: hpoppe@ncar.UUCP
amichiel@rodan.acs.syr.edu (Michielsen) (01/03/90)
In article <1381@umigw.MIAMI.EDU> dnelson@mthvax.cs.miami.edu (Dru Nelson) writes: >The MC145406 requires + and - >5 volts to + and - 12 volts power supply >There >are 3 drivers and 3 receivers per package. > >Recently introduced is the + 5 volt only MC145407P which only requires >+5 volt input supply and generates internally + and - 10 volts to >permit full compliance with the RS-232 spec. There is enough supply >power generated to power an additional MC145406 device if so desired. >The MC145407 has three drivers and three receivers also. > Has anyone seen pricing for these chips ? (quan 1 & quan 1K) Does anyone know if SK or ECG or other has already or plans to product a replacement (copy) ? Has anyone found these (starting to be or whatever) being stocked on the local level at electronic supply or hobby shops or something ? Is the old maxi 5 Vcc rs232 driver chip directly replaceable by the MC145407, or did MC pick some different pin out ? AL
elliott@optilink.UUCP (Paul Elliott x225) (01/03/90)
In article <MZb4w2600WB88M=4wv@andrew.cmu.edu>, kg19+@andrew.cmu.edu (Kurt A. Geisel) writes: > I am trying to convert a TTL signal into an RS-232 signal. I was > under the impression that this can be done simply with the MC1488 > monolithic quad serial line driver. Here is my set-up: > > 2 |----------| 3 > TTL ---------->| |---------> RS-232 > 1 | MC 1488 | 14 > -5 V --------->| |<--------- +5 V > 7 | | > GND ---------->|----------| > > What I get: > > 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. The MC1488 requires a split-supply of at least +/- 9V to yield RS-232 output levels. (with 9V, you get +/- 7V typ. out). I am puzzled by the output level you get with +5V TTL in, however. Looking at the internal schematic of the part, it seems that you should get a negative output of about -3.6V. Perhaps there is a wiring error? Anyway, if you don't have the higher Voltage supplies available, may I suggest trying the MAX-232 transceiver from Maxim (*). It has an on-board charge-pump (using external capacitors) that boosts a +5V supply to +/- 10V for driving the RS-232 line, and is very easy to use. This part is being second-sourced or cloned by other manufacturers. * Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 -- Paul M. Elliott Optilink Corporation (707) 795-9444 {pyramid,pixar,tekbspa}!optilink!elliott "I used to think I was indecisive, but now I'm not so sure."
henry@utzoo.uucp (Henry Spencer) (01/03/90)
In article <5834@ncar.ucar.edu> hpoppe@bierstadt.UCAR.EDU (Herb Poppe) writes: >Maxim MAX232 >Motorola MC145407 > >Question: >Are either/both of these parts CMOS? Yes, both. However, if your question really is "is their power consumption very low?", you had better ask that explicitly. There's CMOS, and then there's CMOS. Most modern microprocessors, some of which run too hot to touch, are CMOS -- they'd melt if they were NMOS. CMOS technology is used in many parts which are not "classical" ultra-low-power CMOS. The MAX232 pulls 5-10 mA with no load. I haven't got a 145407 datasheet handy. -- 1972: Saturn V #15 flight-ready| Henry Spencer at U of Toronto Zoology 1990: birds nesting in engines | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
ISW@cup.portal.com (Isaac S Wingfield) (01/03/90)
Kurt Geisel writes: >Thanks for all the help. The consensus seems to be: it should work, >but you really should be using +/- 12v. Well, this is very temporary >and very hardware specific, so I think I'll stick with it for now. >The port I'm trying to drive seems to accept stuff well under the 232 >spec. In fact, the 1489 (RS-232 receiver, the most likely chip you're talking to), is usually biased so that the threshold voltages are about 1V and 3V (it's specs are rather loose). You have to add a negative bias in order to force the lower threshold below 0V, and most designs don't bother. The upshot of this is that *in most cases* you don't need a special driver at all - just use a CMOS inverter. I like to wire two in parallel for lower impedance. TTL thresholds are a little close to the 1489's for comfort. BTW, use another CMOS inverter for the receiver: RS-232 signal goes through 100k or so to limit current right into the inverter, and put a couple of diodes from GND to input and from input to VCC, both cathodes pointing up, to clamp the input for safety. For best noise immunity, use a Schmitt inverter. Not commercial quality, I know, but I've been doing this for years, and have yet to have a malfunction or part failure. Isaac isw@cup.portal.com
john@frog.UUCP (John Woods) (01/04/90)
In article <1640@rodan.acs.syr.edu>, amichiel@rodan.acs.syr.edu (Michielsen) writes: > In article <1381@umigw.MIAMI.EDU> dnelson@mthvax.cs.miami.edu (Dru Nelson) writes: > >Recently introduced is the + 5 volt only MC145407P which only requires > >+5 volt input supply > Has anyone found these (starting to be or whatever) being stocked on the > local level at electronic supply or hobby shops or something ? The MAX232CPE (the other 5V-only RS232 chip) is available from Active Electronics; hence these chips in general should be available from hobbyist places. > Is the old maxi 5 Vcc rs232 driver chip directly replaceable by the > MC145407, or did MC pick some different pin out ? One would think it is different, unless the 145406 had pins to connect capacitors just for art's sake :-). -- John Woods, Charles River Data Systems, Framingham MA, (508) 626-1101 ...!decvax!frog!john, john@frog.UUCP, ...!mit-eddie!jfw, jfw@eddie.mit.edu Happiness is Planet Earth in your rear-view mirror. - Sam Hurt
aaron@cbnewsh.ATT.COM (aaron.michael.chesir) (01/04/90)
In article <MZb4w2600WB88M=4wv@andrew.cmu.edu>, kg19+@andrew.cmu.edu (Kurt A. Geisel) writes: > Help a poor non-EE : > > 2 |----------| 3 > TTL ---------->| |---------> RS-232 > 1 | MC 1488 | 14 > -5 V --------->| |<--------- +5 V > 7 | | > GND ---------->|----------| > > What I get: > > 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. > Your problem is that the MC1488 takes +- 12 (TWELVE) Volts, not +-5V. Aaron Chesir ..att!twitch!aaron . aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa PS - The above lines are here to fulfill my system's requirement that a (this) response to an article have more characters than the original posting. Can I override this requirement?
markz@ssc.UUCP (Mark Zenier) (01/06/90)
In article <7041@cbnewsh.ATT.COM>, aaron@cbnewsh.ATT.COM (aaron.michael.chesir) writes: > Your problem is that the MC1488 takes +- 12 (TWELVE) Volts, not +-5V. Actually, Motorola says the chip will work down to +7, -2.5 volts, but +/- 6 seemed to work fine. markz@ssc.uucp
cook@stout.ucar.edu (Forrest Cook) (01/08/90)
In article <MZb4w2600WB88M=4wv@andrew.cmu.edu> 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