From: wrb@cbnews.cb.att.com (wallace.r.blackburn)
Subject: Re: Serial Interface; Kenwood TS-440 & 850
Organization: AT&T
Distribution: usa
Date: Fri, 20 Nov 1992 14:06:13 GMT

In article <1992Nov18.215539.22692@cbnewsj.cb.att.com> k2ph@cbnewsj.cb.att.com (The QRPer) writes:
>From article <1992Nov18.192318.28531@cbnews.cb.att.com>, by wrb@cbnews.cb.att.com (wallace.r.blackburn):
>> Whole bunch of stuff removed...
>> 
>> This is kind of risky in a couple of ways.  First, not meeting the RS-232
>> specs is asking for trouble.  A valid mark is -3 to -25V.  While the 0.2V
>> might be accepted as a valid mark, it might get kind of flakey under some
>> circumstances (like right in the middle of a contest!).
>> 
>
>Not meeting the RS-232 specs isn't asking for trouble at all,
>since the 1488 and 1489 quad driver and receiver chips used
>almost everywhere don't meet the specs themselves!  Weren't
>designed to.  As far as going all the way to -25 volts or
>all the way up to +25 volts, you'll never see this.
>
>I know at least two hams with TS-940Ss with the IF-10B installed
>that simply swamped the output of the TxD lead on their computers
>with a 1N4733 5.1-volt, 1 watt Zener diode.  Then, they swapped
>the TxD and RxD leads to the transceiver (simple null modem).
>Guess what, gang, it works.  Worked all contest weekend.  And,
>it continues to work to this day.  This is no surprise as the
>1489 and 1489A quad receiver chips are already TTL compatible
>and the 5.1-volt Zener diode (combined with the 300-ohm series
>output resistor in the 1488) safely forms a RS-232 to TTL
>level converter.  Instead of paying Kenwood 100 bucks for an
>IF-232C, they paid Radio Shack a dollar for a Zener diode.
>
>As far as 0.2 volts "might" be accepted as a valid mark, it WILL
>be by anything using either a 1489 or 1489A receiver chip, since
>they trigger at anything below 1.5 or 2.25 volts.  Which one
>depends on whether it's a 1489 or 1489A.
>
>Lots of equipment could be built less expensively if designers
>looked at the way RS-232 devices are actually implemented instead
>of blindly crossing every t and dotting every i in the standards
>documentation.  I say this as someone who worked with the standards
>community for many years (a goodly portion of the revision from
>RS-232C to RS-232D was my idea).
>

I respect your opinion Bob.  You obviously know quite a bit about RS-232
(or EIA-232-D, or whatever it's called today).  But I just don't agree with
you on this.

I believe your simple interface will work ALMOST all of the time.  As you
stated, the 1488/1489 are used ALMOST everywhere.  As far as PCs go, I
would even bet that they were used absolutely everywhere - 5 years ago.
What about a PC using a chip similar to the MAX232?  A good example is
laptops.  I'm sure many of them are using the new 3.3V level charge-pump 
converters.  Will the TTL levels work with them?  Maybe it will work with
some and not others.  Maybe it will work 95% of the time.

That's the trouble with mediocrity, Murphy knows how to exploit it to the
fullest.  Like maybe on Field Day when you haul out your TS-940 and try to
make it work with your buddy's laptop.  Guess what, gang, it works.  Until
about 2:00 in the morning.

I'm not saying to spend 100 bucks for the Kenwood unit.  A nice interface
using the MAX232 and some optoisolators can be built for $20 bucks or so if
you scrounge.  That $2 spent for the optos might save some repair work on
your $1400 TS-940 too.  The interface also implements RTS/CTS.  I know most
software doesn't use it, but at least two packages do.  Of course, you could 
connect these the same way you did RxD/TxD.

>Time to get off my soapbox now.  :-)
>
Me too.


				Wally Blackburn AA8DX