Mario,
I think there is more to this story. This is purely my opinion after
twelve years writing code and messing with the LPT port.
I always assumed that K1EA used pin 1 (strobe) for the emitter of the
keying transistor because the state of pin 17 (CW out) is unknown when the
computer is started. I'm not sure if this is a random condition or a BIOS
issue, but on many computers pin 17 is high when booted which causes a CW
radio to go key down (very annoying). By keeping pin 1 unasserted, the
logging program can prevent keying until the pin 17 is low. Indeed, if I
recall correctly early versions of CT keyed only pin 1.
Some years later, N6TR introduces PTT control on pin 16. This pin has the
same problem as pin 17 - an undetermined state at startup. To prevent
unintentional PTT assertion at bootup, an duplicate of the CW keying
circuit was used. However, since pin 1 has to be shared now, it can't be
keyed for CW so positive keying on pin 17 is introduced.
I've always been concerned about the current handling capacity of the
circuit connected to pin 1. This was designed as a ~STROBE signal to a
printer, now we hang CW keying circuits and PTT on it. The CW line is
almost certainly low current, but who knows about PTT? You never know -
with certain radio types that line might directly pull in a relay coil.
In most of my CW interfaces now I've added a CMOS logic IC to allow pin 1
to inhibit the CW keying and PTT in the signal path. The output devices
interfacing to the radio can sink directly to ground without the currents
going into the LPT port. One added advantage is that the key-down
saturation voltage is lower, thus ensuring full power out on CW. (Don't
laugh - I tried to use a Darlington output optocoupler to key/PTT one of my
radios and it would not work!).
BTW, CW out has always been pin 17, not 16. Pin 16 is PTT. This is the
way NA has been for years and I've just been copying everybody. I just
checked this against a reasonably recent TRLog manual.
Not to embarrass anyone, but you can't count on WX0B to get the pins
right. He got his NA pinouts second hand and they were incorrect (Jay told
me this).
Jeez...I thought we had all settled on a standard :-(
73,
Dave/K8CC
At 11:15 PM 12/22/01 +0000, Marijan Miletic, S56A wrote:
>I used the voltmeter on LPT port a lot lately!
>
>In early CT versions, just pin 1 was enough for TTL keying as it used
>natural STROBE function going low when activated.
>
>TR decided to key pin 16 with a positive signal. Universal keying circuit
>needed NPN transistor for compatibility between both programs.
>It claimed 50 mA keying capability which is way bellow pin 1 sink ratings.
>
>ARRL handbook announced a circuit which used pin 1 as enable for PTT. It
>used plenty of relays for various switching.
>Writelog was keying both pins 1 and 16 affecting smooth PTT operation in
>commercial SO2R boxes.
>Free N1MMLogger didn't do that with pin 1.
>
>Now we develop SO2R situation with pin 1 permanently low, pin 14 going low
>for Radio B and no power source for my miniature LPT adapter :-(
>
>May I kindly ask for a pin 1 to go low at PTT time and everything will
>work fine in USA and EU!
>
>73 de Mario, S56A, N1YU <http://www.miletic.net>www.miletic.net
>>----- Original Message -----
>>From: <mailto:w5xd@writelog.com>W. Wright, W5XD
>>To: <mailto:TOMK5RC@aol.com>TOMK5RC@aol.com ;
>><mailto:writelog@contesting.com>writelog@contesting.com
>>Sent: Saturday, December 22, 2001 5:33 PM
>>Subject: RE: [WriteLog] 10.69 Fixed the LPT Pin 16 Problem
>>
>>in case anyone would really like to know what happened here...
>>Over the past 12 months or so a couple of folks reported that WL did not
>>handle pin 16 correctly.
>>I checked everything thoroughly and never found a problem in my shack.
>>
>>This month, one kind sole actually put a voltmeter to his LPT port before
>>sending out emails about pin 16.
>>His report was that WriteLog was handling pin 1 differently than
>>"everyone else" (NA/CT/TR).
>>
>>WL 10.29 changes WL's behavior on pin 1 (NOT PIN 16!).
>>
>>Wayne
>>
>>-----Original Message-----
>>From: writelog-admin@contesting.com
>>[mailto:writelog-admin@contesting.com]On Behalf Of TOMK5RC@aol.com
>>Sent: Saturday, December 22, 2001 15:49
>>To: writelog@contesting.com
>>Subject: [WriteLog] 10.69 Fixed the LPT Pin 16 Problem
>>
>>I installed 10.69 last night and now my WX0B SO2R box works as
>>advertised. No more CW on Pin 16. Perhaps we will never know why it
>>happened, but I am a happy camper now.
>>
>>Tom, K5RC
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