View Full Version : More n00b circuit questions

3rd February 2004, 09:32
Hey guys, more circuit questions! Please help!

We tested parallel port inputs on various PC's and it appears that the inputs vary from one computer to another. As in, we would be sending the same signal onto the same input pin on different computer, but different computers would read it differently even though we use the same software. My questions are:

1. Why does this happen in the first place? Wouldn't it be simpler to have it more universal?
2. How would we be able to check this pin configuration in software without having to build a calibration circuit?
3. If we do have to build some sort of hardware circuit to check this pin configuration, what approach should we take?

3rd February 2004, 09:37
may have something to do with ecp/epp/standard for type of parrallel port in computer bios??

3rd February 2004, 12:30
Not all parallel ports are equal.

Older PPorts (before EPP and ECP) are output only. They have 5 pins that can be used as inputs - these are the error bits (paper error/offline/data interrupt ... I can't remember the rest)

So, you have to use pins other than the 8 data bits if you want to be able to read back on any port.

Alternately, you could make sure that all the machines are set to the same type of port (as gt40 said), then make it work for that port type.

- Steve

3rd February 2004, 13:06
yes, that's what me and my partners did. We used the 5 input pins (pin 10, 11, 12, 14, and 15) for input. But if we run the same hardware on other parallel ports, the input value it reads in is different.

For example, in turing... the sample program goes like this...

put parallelget
end loop

if we run this on different computers (different models in the lab), the outputs are different. (for example, one outputs 82, and anothe routputs 102) this happens even if nothing is connected to the parallelport, imo its kinda weird!

3rd February 2004, 17:19
What does your parallelget function look like?

9th February 2004, 13:13
In turing:

put (parallelget)
end loop

13th February 2004, 20:18
bump, I really need your help guys.

me and my partner used this Parallel port driver... http://www.aaroncake.net/electronics/vblpt.htm

I think it has to do with different address for LPT1 for different computer. Anybody know if I am in the right direction?

13th February 2004, 21:39
ok, nvm, forgot this post. I am just gonna build an auto-caliberation circuit lol...

damn, this means i may have to redo all the resistor calculation stuff... whatever

anyways, for my next project, I am just gonna use serial port/USB to interface :rolleyes:

Brian Ellis
14th February 2004, 01:07
Will not the LPT parallel ports be dead in a coupla years or so? And the COM serial ports, for that matter? I've bought 2 printers in the last 2 years. One is USB only and the other (a fully pro laser) offers USB, 10/100 networking and parallel.

The only use I have for parallel/serial ports nowadays is for dongles! Are they not just a legacy destined to follow 8 bit computing?

14th February 2004, 07:08
LOL Brian, I am a high school student. All they teach there is parallel port interfacing, because its the easist to deal with.

Any serial interfcae is harder because they never teach stuff like letches and stuff. Besides, I am learning all these myself. The class is quite basic.