[HomeBrew] Lpt port trouble

[Flowertime01 at wmconnect.com]

Ken,

Your kind of screwed with a simple circuit.
At power on self test, (POST) a part of the bios chip instructions even 
before any software is loaded from a disk into memory test all the ports. All the 
port bits get set as part of the test. If the computer will not complete the 
self test, it will never boot, or will boot with the port disabled because it 
failed the test.

You almost have to go through some kind of an active interface.
An easy (??) out is a four bit flip flop in CMOS logic (powered from the 
computer 5 volts) that resets on power on and needs 4 bits to get a toggle out the 
end on the first time. Then each change of the control line will change the 
out put for you.

You can also invert then and the CLS DSR (any two logic lines you have) to 
work.
Play with the lines and find a pair that the power on logic does not trip the 
gates active. Then you can toggle the control lines to get the logic you need.

You may be able to use another logic line if you are doing your own code.

You may run a 555 timer so that on power on, you get a delay and the signal 
is not passed to the radio until the computer has a chance to boot and the 
software can set the control line inactive.

I had some bright young engineers who tried a short cut on a Navy project and 
it took them about 6 weeks to learn the lessons they missed in school. 

Good Luck 

Roger KC6TRU