SCSI Parity Generator


The following upgrade was originally found on Jo Even Skarstein's homepage.
http://www.stud.ntnu.no/~josk/atari/hardware_mods/parity_gen.html

SCSI Parity Generator
This is the Parity generation logic that solves the problem for those
Atari users that use SCSI adaptors without parity. As you can see it
consists of one single 74HC280 chip. The easiest place to get to the
SCSI signals is the harddisk itself. You can use the four pin
connector's red pin for +5V and the black for GROUND.

This parity generator has been tested with the following adaptors:

   ICD Link 1 (the first type)
   Megafile 44 SCSI adaptor
   Mega STE SCSI adaptor
   Protar SCSI adaptor


Pinout of the 74HC280

         74HC280

       +---\_/---+
    D6 |1      14| +5V
    D7 |2      13| D5
    NC |3      12| D4
 INPUT |4      11| D3
  EVEN |5      10| D2
   ODD |6       9| D1
   GND |7       8| D0
       +---------+

The logical schematic for added parity generation

  74HC280                    SCSI-bus
 +--------+                  +-------+
 |     P8 | D0------------D0 | P2    |
 |     P9 | D1------------D1 | P4    |
 |    P10 | D2------------D2 | P6    |
 |    P11 | D3------------D3 | P8    |
 |    P12 | D4------------D4 | P10   |
 |    P13 | D5------------D5 | P12   |
 |     P1 | D6------------D6 | P14   |
 |     P2 | D7------------D7 | P16   |
 |     P6 | ODD------ PARITY | P18   |
 |        |                  +-------+
 |    P14 | +5V
 |        |
 |     P3 | NO CONNECTION
 |     P5 | NO CONNECTION
 |        |
 |     P4 | INPUT--+
 |     P7 | GND----|
 +--------+        |
                  GND


copyright (c)1996 Martin Graiter. Non-commercial use granted to all
Atarians of the world! Questions etc. to: magrait@algonet.se


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