Tinkering with Parallel ports

 

Ah the weekend, again. I feel like tinkering a bit, so let’s tinker with Parallel ports. Actually, the idea got embedded when a few days earlier when I read a post on channel 9. So the first thing was to build an LED probe – I couldn’t find my old one, but building a new one won’t be hard.

About 15 years ago, I did some work looking at ways of producing good, but ‘cheap’ sound from the Business computers of the day – for the young amongst you, back then sound cards where optional, as they typically cost over $150.00 each (probably more like $250). After quite a bit of (snail) research (the Internet was just starting up here, in Australia), I ended up producing initial designs which used the Parallel port. I might dig up the design I did using the, then, new low-voltage Microchip PIC device. Anyway, my memory is not that good, so I did have to double check that I was about to use the right pins.

Pin #	Return	Name	Description
1	18	/STROBE	Data Strobe
2	19	D0	Data bit 0
3	19	D1	Data bit 1
4	20	D2	Data bit 2
5	20	D3	Data bit 3
6	21	D4	Data bit 4
7	21	D5	Data bit 5
8	22	D6	Data bit 6
9	22	D7	Data bit 7
10	23	/ACK	Acknowledge
11	23	BUSY	Busy
12	24	PE	Paper Empty
13	24	SEL	Select
14	24	/AUTOFD	Autofeed
15	25	/ERROR	Error
16	25	/INIT	Initialise
17	25	/SELIN	Select In

I dug through my box-of-bits, and dug out the eight 3mm LEDs and resistors, some vero board and a DB25m connector. A couple hours later (funny how time flies when your doing menial tasks like bending the LED leads to the right height, etc), I had a simple Parallel LED probe. The eight LEDs being directly driven by each of the eight data bit signals through 360 Ohm resistors (these unusual resistors where scored from a surplus box, about 20 years ago – big bag).

OK, that’s my Electronics appetite appeased. Now for a light show.

With Windows NT and later versions of Windows, user-mode applications can no longer access the hardware directly. But as I noted in my channel 9 response, you can use a Virtual Machine running the older Windows 9x operating systems, and just let the Virtualisation software translate it for you. As I wasn’t sure wether Microsoft’s Virtual PC would also work, I installed Virtual PC 2007 on the now familiar, 1.7GHz Celeron System running Vista Enterprise. After some stuffing about, I managed to convert one of my VMWare disk images, etc. I then looked into wether I could install Visual C++ 2005 Express into the Windows 98 SE virtual machine, but then chickened out, and installed Dev-C++, instead.

As it turned out, I needed to hack one of the headers, in this case conio.h, as I wanted to match Microsoft – the whole idea of Mingw and therefore Dev-C++ is to compile using Microsoft’s MSVCRT DLL(s):

#if defined(__MSVCRT__ || __MINGW32__ )
  int __cdecl _inp(unsigned short);
  unsigned short __cdecl _inpw(unsigned short);
  unsigned long __cdecl _inpd(unsigned short);
  int __cdecl _outp(unsigned short, int);
  unsigned short __cdecl _outpw(unsigned short, unsigned short);
  unsigned long __cdecl _outpd(unsigned short, unsigned long);
#endif

Here is a simple program to get you started. I simply hard-coded the I/O port address for the first Printer port (LPT1:). I’ve embedded a link to a soapbox video, so lets see how good you are figuring out why the LEDs turn on and off the way they do:

#include <windows.h>
#include <conio.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
  int    i, n = 8 * 10;

  _outp( 0x378, 0 );
  Sleep(3000);

  for(i=0; i < n; i++)
  {
    _outp( 0x378, 1<<(i & 0x7) );
    Sleep(150);
  }

  _outp( 0x378, 0xff );
  Sleep(150);

  for(i=0; i < n; i++)
  {
    int d = i & 0x7;
    d = (i & 8) ? (7 - d) : d;
    _outp( 0x378, 1<<d );
    Sleep(150);
  }

  _outp( 0x378, 0xff );
  Sleep(150);

  for(i=0; i < n; i++)
  {
    int d = (i & 0x3)<<1;
    d = (i & 4) ? (7 - d) : d;
    _outp( 0x378, 1<<d );
    Sleep(150);
  }

  // Done.
  puts("\nPress enter to exit");
  getchar();
  return 0;
}

Now a further challenge.

In the last two loops, I have a ‘?:’ conditional expression. eg d = (i & 8) ? (7 – d) : d;  Can you think of equivalent expression(s) which do not have conditionals ?