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Atom harddisk interface

Finally A schematic of my internal harddisk interface for the SAM (or with some changes for any other 8-bit computer). The interface consists of a 16 to 8 bit bus converter,address decoder, and a bus stabelizer. The later one was added to make the rather slow z80 bus interface with the fast IDE bus. This bus stabelizer (IC1) is a transparent latch which 'samples and holds' the required signals for the address decoder when the DISC2 signal becomes active (this could be IORQ in other systems).


ATOM Schematic


This interface works also with two harddrives (MASTER/SLAVE) or harddrive/CD-ROM combination. When using a harddrive build in your system and like to add a external one then I would recommend to use ome of the free outputs of IC8 to use as a alternate chipselect line for the external harddrive so you can have a MASTER/MASTER configuration with all kinds of harddrives without messing around with jumpersettings (This option is not supported by BDOS).


In order to use this harddisk interface you need BDOS. Please goto the BDOS section for more info.

It's als possible to boot from hardisk disk directly by replacing the SAM's ROM with one which contains my 80 byte boot code. Go to the BOOTROM section for more info.


1 32 pin wide Female Euro connector with pins at rows A and B (a 64 pin wide will also work if you cut it in half)
1 40 pin male ID connector
1 22 uF / 16V Electrolitic capacitor
8 22 nF Ceramic capacitor
1 10 k resistor
2 1N4148 Diode
1 74HCT573 (IC 1)
1 74HCT138 (IC 2)
3 74LS245 (IC 3,4 and 6)
3 74hct574 (IC 5,7 and 8)
1 470 Ohm resistor


The interface takes it power from the SAM. A single 2 inch drive which consumes not more than 500 mA can also be powered by SAM. But Other drives must be powered by a separate powersupply. A PC AT powersupply will do fine. I myself use a Amiga 500 Powersupply which powers both my SAM and a harddisk.

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