Such adapter is limited to access only 1GB on SCSI hard disks. In time
when it was designed it was pretty good, but now is even hard to find
drives under couple GB (used ones). 1GB limit is result of fact that
adapter allows sending of 5 bit SCSI commands only. Those are commands
with codes 0-$1F .
My idea was to allow sending of 6-bit commands. With help of schematic of similar adapter, lot of patience and experimenting I did it.
Now, very large drives are accessible - in theory up to 2000GB, but biggest one what I have is 18GB, and it works fine.
2 reconnections on board are required. right in middle is mark A (red) - there need to cut pcb. line between pin 5 of IC and hole.
Down by ACSI PAL need to bend pin 6 of PAL chip so that it will go out of socket, and connect it with pin 3 - mark B.
A expands commands on 6 bits. B ensures that adapter will activate regardless of state of bit 5 by command phase.
There is 2 problem by this solution: TOS 2.06 locks SCSI drive when it autoboots not . It will happen only once - before installing autoboot driver (from floppy), but hard drive must became ready to allow driver install. Solution is to connect button (taster) between SCSI reset line (pin 40) and GND. Pressing it will reset SCSI drive and it will work. Then may install autoboot driver. After it drive lock will not happen, even when disable driver autoload (with ALT key) - I added some code in loader which prevents drive lock.
Updated: it is possible to use together with external drive - I tested with Satandisk set to target #5. But newer driver version is required - it is not published yet...
Parity generator:
Most of modern SCSI drives works only with parity on - I saw only IBM drives where parity can be disabled. In praxis it means that such drives will not work with our adapter.
Solution is again simple and cheap: adding 74HCT280 parity generator chip to board. On pic, chip is half visible near to pins 1-2 of SCSI connector. I put it there, because could solder 6 data lines directly to board.
Connecting of pins goes like this:
So modified adapter will work with existing drivers (Hddriver, ICD), but still only up to 1GB.
Special driver is required to get benefit:
Driver for modified adapter
Driver specs:
P. Putnik, October 2007, April 2009.
My idea was to allow sending of 6-bit commands. With help of schematic of similar adapter, lot of patience and experimenting I did it.
Now, very large drives are accessible - in theory up to 2000GB, but biggest one what I have is 18GB, and it works fine.
2 reconnections on board are required. right in middle is mark A (red) - there need to cut pcb. line between pin 5 of IC and hole.
Down by ACSI PAL need to bend pin 6 of PAL chip so that it will go out of socket, and connect it with pin 3 - mark B.
A expands commands on 6 bits. B ensures that adapter will activate regardless of state of bit 5 by command phase.
There is 2 problem by this solution: TOS 2.06 locks SCSI drive when it autoboots not . It will happen only once - before installing autoboot driver (from floppy), but hard drive must became ready to allow driver install. Solution is to connect button (taster) between SCSI reset line (pin 40) and GND. Pressing it will reset SCSI drive and it will work. Then may install autoboot driver. After it drive lock will not happen, even when disable driver autoload (with ALT key) - I added some code in loader which prevents drive lock.
Updated: it is possible to use together with external drive - I tested with Satandisk set to target #5. But newer driver version is required - it is not published yet...
Parity generator:
Most of modern SCSI drives works only with parity on - I saw only IBM drives where parity can be disabled. In praxis it means that such drives will not work with our adapter.
Solution is again simple and cheap: adding 74HCT280 parity generator chip to board. On pic, chip is half visible near to pins 1-2 of SCSI connector. I put it there, because could solder 6 data lines directly to board.
Connecting of pins goes like this:
| 74HCT280 |
SCSI
bus |
Function |
| 1 |
14 |
D6 |
| 2 |
16 |
D7 |
| 3 |
- |
NC |
| 4 |
GND |
GND |
| 5 |
- |
NC |
| 6 |
18 |
Odd parity |
| 7 |
GND |
GND |
| 8 |
2 |
D0 |
| 9 |
4 |
D1 |
| 10 |
6 |
D2 |
| 11 |
8 |
D3 |
| 12 |
10 |
D4 |
| 13 |
12 |
D5 |
| 14 |
- |
+5V |
So modified adapter will work with existing drivers (Hddriver, ICD), but still only up to 1GB.
Special driver is required to get benefit:
Driver for modified adapter
Driver specs:
- Partition drive on PC, use on ST and PC - easy file transfer.
Requires BigDOS (included).
- Handles up to 14 partitions on SCSI disk via
modified ACSI-SCSI adapter in Mega STE.
- 2000GB max accesible on drives - using SCSI commands Read(10) and
Write(10) with 32-bit LBA addressing .
- Max FAT16 partition size 2GB - boot partition too (no 15MB
limit
and similar)
- XHDI support - may work with FAT32 partitions under Mint
- Autoboot on Atari from DOS partitioned drives - easy and quick install. Installer from floppy
- Any partition may be selected to be C (boot partition) by booting - put games on one part, Mint on another - easy switch.
- Option for HOLE creation by driver loading - better compatibility
with some old games.
- Speed is up to 1000-1250KB/sec depending from adapter and attached drive.
- No support for removable drive change without restart.
P. Putnik, October 2007, April 2009.