***************************************************************
  **                                                           **
  **   How to connect an IDE-harddisk to the Atari Portfolio   **
  **            through the parallel interface                 **
  **                                                           **
  ***************************************************************
  Edited 19.10.1998 by Klaus Peichl (peichl@usa.net)

There's a new driver called POFOIDE.SYS written by Peter Faasse that
can control an IDE harddisk drive through an Intel 8255-IO-controller
like used in the Atari parallel interface. 24 control signals plus
ground have to be connected according to the below scheme.

     8255               Sub-D-25                IDE
  pin   name           pin   name            pin   name

    5   Port A.0 ------  2   Data 0  -------- 17   Data 0
    4   Port A.1 ------  3   Data 1  -------- 15   Data 1
    3   Port A.2 ------  4   Data 2  -------- 13   Data 2
    2   Port A.3 ------  5   Data 3  -------- 11   Data 3
   44   Port A.4 ------  6   Data 4  --------  9   Data 4
   43   Port A.5 ------  7   Data 5  --------  7   Data 5
   42   Port A.6 ------  8   Data 6  --------  5   Data 6
   41   Port A.7 ------  9   Data 7  --------  3   Data 7

   20   Port B.0 ------  1   Strobe  --------  4   Data 8
   21   Port B.1 ------ 14   Auto Feed-------  6   Data 9
   22   Port B.2 ------ 16   Init    --------  8   Data 10
   24!  Port B.3 ------ 17   Select in------- 10   Data 11
   25   Port B.4 ~~~~~~ 18*  (Gnd)   -------- 12   Data 12
   26   Port B.5 ~~~~~~ 19*  (Gnd)   -------- 14   Data 13
   27   Port B.6 ~~~~~~ 20*  (Gnd)   -------- 16   Data 14
   28   Port B.7 ~~~~~~ 21*  (Gnd)   -------- 18   Data 15

   16   Port C.0 ------ 12   Paper out------- 35   Address 0
   17   Port C.1 ------ 13   Select  -------- 33   Address 1
   18   Port C.2 ~~~~~~ 22*  (Gnd)   -------- 36   Address 2
   19   Port C.3 ------ 15   Error   ---|>o--  1   /Reset
   15   Port C.4 ------ 11   Busy    ---|>o-- 37   /CS 0
   14   Port C.5 ------ 10   Ackn    ---|>o-- 38   /CS 1
   13   Port C.6 ~~~~~~ 23*  (Gnd)   ---|>o-- 25   /IO Read
   11!  Port C.7 ~~~~~~ 24*  (Gnd)   ---|>o-- 23   /IO Write

			25   Gnd     ----+---  2   Gnd
					 |--- 19    .
					 |--- 22    .
					 |--- 24    .
					 |--- 26    .
					 |--- 30    .
					 +--- 40   Gnd

			  +5V---\/\/\--->|--- 39   /ACT (/Busy)
				  R    LED             
  Notes:

  1. The pin numbers marked with "!" are correct, there is a gap.
     The numbers refer to the PLCC-version of the 8255 used in the
     Atari parallel interface. They are printed on the circuit
     board there.

  2. The pins marked with "*" are normally connected to Gnd.
     You can modify your parallel interface to provide all 24
     signals at the connector by connecting these pins directly
     to the 8255 (marked with "~~~~~~"). You can also insert
     resistors to limit an accidental shortcut current. I used
     resistors of 330 Ohm which works very well.
     Unfortunately, pins 18 to 25 of the Sub-D-25-connector in 
     the interface are grounded from both sides of the circuit
     board. The shown assignment is just a proposal (I did it
     this way).
     
     Be aware that many devices (like printers) connected to the
     parallel interface shortcut pins 18 to 25. Do not connect them
     to the manipulated interface! To avoid the shortcuts, you could 
     make an adaptor cable which has all Ground-wires connected to
     pin 25.
     
  3. In the IDE-cable, Data 0 through Data 7 and Data 8 through
     Data 15 are "interlaced and mirrored".

  4. In the IDE-cable, the wires 2,19,22,24,26,30,40 are Ground.
     At least one, preferably all must be connected to ground on
     the Portfolio side.

  5. The last five signals must be inverted. A 7404 or 7414 logic IC
     can do this (same pinout).
       7404 = 6 inverters
       7414 = 6 Schmitt-trigger-inverters
     Probably any 74xx04 or 74xx14 will work, but CMOS-technology 
     (xx=HC or HCT) will draw a much lower current.
     
			+----\/----+
		    1A -| 1     14 |- VCC (5V)
		    1Y -| 2     13 |- 6A
		    2A -| 3     12 |- 6Y
		    2Y -| 4     11 |- 5A   7404/7414
		    3A -| 5     10 |- 5Y
		    3Y -| 6      9 |- 4A   A=INPUT
		   GND -| 7      8 |- 4Y   Y=OUTPUT
			+----------+
			 (top view)
  
  6. Optionally, an LED can be connected to pin 39 of the IDE-
     connector like shown. The resistor value should be 220 Ohm
     for normal LEDs but can be much higher for a low current
     type.


  Pin layout of the parallel port Sub-D-25-connector
  ==================================================

	------------------------------------------ 
	\ 13 12 11 10  9  8  7  6  5  4  3  2  1 / 
	 \  25 24 23 22 21 20 19 18 17 16 15 14 / 
	  -------------------------------------- 
	  (female, view onto the interface unit)


  IDE-connector
  =============

    1                  39    odd-numbered pins 
    .................... 
    .................... 
    2                  40    even-numbered pins 
 
  Take a standard IDE-cable for PCs and cut off one end. 
  The numbering of the wires is simple: Start with 1 at the marked
  wire (mostly partially red) and count the wires until you end with
  number 40 at the other side of the ribbon cable.

  Most of the wires can be soldered directly to a male Sub-D-25-
  connector. Like shown, the wires 1,23,25,37,38 must be inverted.
  All signals to be inverted are control signals, i.e. the inverter
  input (A) goes to the parallel port and the inverter output (Y)
  goes to the IDE connector.
  I recommend to place the inverter IC near the IDE-connector and to
  take its 5V-supply from the harddisk power supply. Gnd should not
  be a problem, as there are enough ground-lines in the cable.