LPT-port description:

DSUB-25 (male) view from backside:
  -------------------------------------
( 1  2  3  4  5  6  7  8  9 10 11 12 13 )
 ( 14 15 16 17 18 19 20 21 22 23 24 25 )
   -----------------------------------

The female connector at the PC has the same pinnumbers, but the 
view would be from front then.

8-Bit wide DATA bus: (base adress)
Pin 2-9 D0-D7 <these go to the interface

4-bit wide bidirectional bus: (base address + 1):
Pin 1  /Strobe      Bit 0
Pin 14 /Auto        Bit 1
Pin 16 /Init        Bit 2
Pin 17 Select       Bit 3
		 Never set the highest Bits in this Byte to 1
		 The system will crash.
	
5 Bit wide INPUT Port: (base +2)
Pin 15 /Error       Bit 3
Pin 13 Online       Bit 4
Pin 12 Paper Empty  Bit 5
Pin 10 /Acknoledge  Bit 6
Pin 11 Busy         Bit 7

Pin 18,19,20,21,22,23,24,25 GND (connect to interfaces GND!)

The four pins of the bidirectional port will be used 
in the expanded poly/multiphonic interface for adressing individual
voices / channels.

A neat trick to prevent Windows from trying to "print" to the 
interface is to put a 1 on the BUSY line when the interface 
is powered up. 

HINTs: To prevent damage of your $2000 PCs on-board LPTs,
get yourself a cheap Multi I/O card first, or use 
an old 286/386 or something for the tests. 

But if you are careful there won't be any trouble, just check  
that the lines that go from the interface to the PCs are not 
shorted nor connected to 5 or 15 V. (No solder blobs!)

You can use QBASICs INP and OUT instructions for testing and 
adjustment: assumed you use the LPT at adress 0x278
type OUT &h278h,0 and measure the value at the output. 
(Should be about 0V) then type OUT &h278,120 and adjust the 
output to 10V + your initial value.


Have fun, and make real good music.

Rene

