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Author Topic: Parallel port not working - my solution  (Read 2273 times)

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Parallel port not working - my solution
« on: July 10, 2009, 05:08:02 AM »
Hi All,

I am in the process of installing CNC on my HBM20 mill and I (finally) nrezsolved a problem last night, the solution for which may aid others.

My PC was bought on eBay (51€!) with a 1.7 GHZ AMD processor and 1GB of RAM. The original machine had XP loaded but also a lot of other video and media hard and software. Consequently I restarted with a clean disk and a clean install of XP. Initially this would not allow a stable operation of the test program, usually masses of lines followed swiftly by a complete lock up requiring a power off restart.
I resolved this by applying all of the solutions in the optimisation document along with a complete reload of XP. This cured the stability problems and also gave me a near perfect result from the test.

Then I attached my breakout board (supplied unbuilt from Marcus electronics in Germany - I am a former electronics engineer so building this was not a major effort) and decided to check the outputs before attaching motors etc.
I found no signals at the stepper driver end, nor any signals coming out of the parallel port. The lines were observed with a combination of normal and storage scopes.
To cut a long and tedious story short, I eventually looked in the BIOS setup and discovered that the parallel port was set for EPP+HPP (I think...) and that there was an option for 'standard'. Changing this and a further reboot resulted in signals all over the place exactly when I wanted them.

I have not seen this issue mentioned anywhere else, perhaps I didn't look hard enough though!

BTW, when looking for signals, I didn't use the jog controls but just set a G0 to say +200 so that I had a constant stream of pulses, allowing me to use both hands for hunting down the signals.

Re: Parallel port not working - my solution
« Reply #1 on: July 20, 2009, 07:57:10 AM »
Update after a looooooonnng weekend trying to make things work:
Parallel port is now back to the original setting, the culprit appears to have been a 'parallel' printer cable that had the full 25 connections but which were mirrored between the two connectors. I guess I should have spotted that one but....
Cured that by cutting and resoldering 25 connections. Very dull 45 minutes. Since the signal connections are more or less centred on the connector, most of the signals were getting through but in a peculier order.

Actual problem (after getting the signals appearing on BOB correctly) turned out to be the clock pulse width. The default setting of 2us (?) was not long enough to get through the opto couplers on my Chinese CW230 drivers. Viewed from the scope the input switched nicely but the output barely dipped. The penny dropped when I downloaded the data sheet which talks of a reaction time of 3us. As soon as I turned up the pulse width, everything sprang into life.

Hope this helps anyone else out there.


Offline Sam

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Re: Parallel port not working - my solution
« Reply #2 on: July 20, 2009, 01:41:53 PM »
Thank you for your contribution, Simon.
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."