13.2.4 Parity Gen

Ein Parity-Generator für ältere Hostadapter

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

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copyright (c)1996 Martin Graiter
Non-commercial use granted to all Atarians of the world!

Questions etc to: magrait@algonet.se