Re: Compters without printer port

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Andrew Mathison" <andrewdavid.mathison@...> wrote:

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> Dear TOM caudle
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> I like a lot of what you are saying and yes, generally you have to be really "rough" to do permanent damage to a MODERN PC.
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> But many here use older PCs or Laptops which might not be as robust as something new(er)....
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> The point I was also trying to make, which you appear to have completely overlooked is that if something is pulling too much "source" current from a PP output pin AND the BIOS boot checks for such things as possible shorts on output pins (amongst other things!), then the PC may stop booting as a safety precaution, seeing that as a short.

The PC is not smart enough to measure current draw from a card or device. The parallel chip will not source enough current to drag down the power supply. Nasty blus smoke would result since the power supplies can source LOTS of current. Post does go through and wiggles port bits, but I would expect an error during POST if it saw a hardware problem it could detect.

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> The original poster has already said that with the cable removed it then boots....! WOW! this info must count for something....

I doubt it's just something physical sitting out on the port. Stranger things have happened but it's more likely a driver issue. Windows has limited capability to detect a hardware issue. It goes out and reads the ROM addresses and trys to detect address conflicts.

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> Maybe a high voltage on an input pin can do the same thing, that is also possible.....
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> Whatever, the boot does not like the situation with the cable connected for some reason or another, but I am too far away to be able to prove exactly what it might be.....so I expect are you too!!

Correct, but I have 25+ years working with PC's and PC hardware. I did a tour as a design engineer at a PC card manufacturer (for original IBM PC's and Compaq's). One product (and problem) I was involved with was a Parallel/Serial expansion card that was having field failures if you turned the printer on with the PC off.

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> Not overstressing the PP in either direction is what makes things work ALL of the time. All you can really RELY on is a 7400 output capability, taking chances on anything else will often lead to problems..

7400 series have output specs all over the spectrum. Typical logic chips (gates) have lower fanouts, the assumption being that they are driving other gates and logic, not heavy loads. Other chips are classified as Bus Drivers and have sink and source capabilities much higher. The 74HC541 chips we use in our cards are rated at 50ma per gate source and sink. Inputs are high impedance and have Schmidt inputs to clean up the input signal. Even the older LS series were rated at 25ma and could withstand a direct short on any output.

...

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> I mentioned the Opto isolators as many feel they are a good idea (if properly designed they are!), but I seldom see any PP to Opto designs that truly take into account the 7400 output characteristics....sadly.

You need to do some study on the 74HC and 74HCT chips and understand that most BOB providers know the difference between the chips and which to use as an interface to the outside world.

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> For anyone like yourself with probably a lot of experience, not a problem, but maybe the OP is slightly out of his depth and asking for us to help him for that reason......I did not get the impression that you helped him in any way with what you wrote, unless he was as experienced as you probably are, then he would probably not have posted in the first place!!!

My post was not an attempt to show how smart I am or to play "I-know- more-than-you" games. It was to clear up misinformation.

Giving answers based on incorrect data performs less help than no answer at all. My post was not so much to help him with the parallel port problem than it was to not send him off in the wrong direction

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> Try initially putting yourself in his position, then I am sure you/we all can help him much better......
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> What do you say to that?

I spend the vast majority of my time explaining complex concepts in CNC to users that are skilled in other areas (machinists, welders, fabricators) I have been the instructor for classes on basic CNC and for guys building their own CNC machines.

Personally, because time is valuable and hardware is cheap, I would either swap out the parallel card, swap out the computer, or go to a computer with a built in port. I have been buying 3GHz Pentium 4 1G RAM , refub computers with XP Pro loaded and a new keyboard and mouse for 139.00 to 169.00 off Ebay. There are a couple of stores that specialize in refurbished PC's (HP's and Dells). They all have built in parallel ports. They come ready to load your controller software (MACH or other). We have several in the shop running Linux and EMC2 as well.

TOM caudle
www.CandCNC.com

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