The ATOM Hard Disc interface is an internal IDE hard disc interface that fits to the Sam Drive connector.
The interface consists of a 16 to 8 bit bus converter, address decoder and a bus stabiliser to make the rather slow Z80 bus interface with the fast IDE bus.
The interface takes it power from the SAM. A CF card or 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 power supply.
The ATOM is merely the IDE interface, the operating system to drive it is B-DOS.
This is the second IDE interface in wide use, the fist being Nev Young's SD IDE interface that ran HDOS.
A popular media to use rather than a full IDE drive is a Compact Flash (CF) card which prompted the development of the Atom-Lite.
See Edwin's ATOM Page for full details.
Finally A schematic of my internal hard disk 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 stabilizer. The later one was added to make the rather slow Z80 bus interface with the fast IDE bus. This bus stabilizer (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).
Schematic
See attached.
Notes
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).
Software
In order to use this harddisk interface you need B-DOS. Please goto the B-DOS 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, see HD Boot ROM
INTERFACE COMPONENTS
| 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) |
| FOR EXTRA DRIVE LED (OPTIONAL) | |
| 1 | 470 Ohm resistor |
| 1 | LED |
POWER SUPPLY
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 power supply. A PC AT power supply will do fine. I myself use a Amiga 500 Power supply which powers both my SAM and a hard disk.
