This is a very preliminary doc. for a SCSI interface for the AMIGA.
I know that it is fragmented, but I am trying to get something together
quickly. Feel free to send me your comments.
At the present time this design does not support DMA or AUTOCONFIG'ing.
The "net-list" also includes parts for an optional 2 meg. memory add-on.
At this time the memory does not work! I have to check my equations and
analize that section of the board. The memory section does NOT upset the
AMIGA or the SCSI interface. There are no special considerations when
building the board. It runs off of the AMIGA's power supply and plugs
into the EXPANSION PORT .
The board uses 1 special part: NCR53C80 (sorry about that.)
I used it because it handles most of the SCSI interface, and eliminates
alot of "LS" chips. (The NCR53C80 is the CMOS version of the SCSI
controller used by APPLE and most other venders!)
Building the board
WARNING ! This board plugs into the expansion port! That port is directly
connected to the CPU and other chips in your AMIGA. Care must be taken so
as not to short anything to +5v or gnd as that may DESTROY your AMIGA.
The circuit and design concepts are sound, but YOU are in control of
your machines destiny. This project is NOT for the casual hacker.
REMEMBER, Don't yell at me if you break your machine!!!
On the lighter side, my board worked the first time it was turned on.
It must be easy if I didn't make any errors... Just take your time and all
will be OK !
After deciding where to locate all of the parts, use the "net-list" to
wire it. I suggest doing all of the wiring to the board before installing
the IC's. Remember that the NCR53C80 is sensitive to static, so be careful.
Also before installing IC's it is a good practice to check the power and
gruond pins on all chip sockets.
PART# LOC USE
74LS688 ....................... Z1 ......... ADDRESS DECODER
74LS139 ....................... Z2 ......... ADDRESS & R/W DECODER
NCR53C80 ...................... Z3 ......... SCSI INTERFACE
7406 .......................... Z4 ......... INTERRUPT BUFFER
74LS244 .................... Z6 Z7 Z8 ...... MEMORY ADD. MUX
PAL20RA10 ..................... Z5 ......... MEMORY CTRL PAL
AMIGA CONNECTOR ............... P1 ......... 86 PIN
SCSI CONNECTOR ................ P2 ......... 50 PIN
MEMORY CONNECTOR .............. P3 ......... 60 PIN
NOTE: DO NOT INSTALL U4,U5,U6,U7,U8 AT THIS TIME.
If you want to wire it, go ahead the DRAM will be comming soon!
The reason for the 74LS688 (8 bit comparitor) is to allow for upgrading
the board for AUTOCONFIG'ing. I don't plan to do this until I get the
important work done (DRAM & CLOCK). It is not hard to use this way,
you have to "install" the board anyway. The advantage of AUTOCONFIG
is that the AMIGA decides where in the memory the board resides.
This is not a problem since it is the only board in the system.....
The PAL (Z5) is used to control the DRAM. It is not needed at this point
so don"t worry about it.
The 'LS139 is used to decode addresses intofour 16K blocks.
1: $800000 is the NCR53C80
2: $801000 is the PSEUDO DMA
3: $802000 is for the CLOCK (not done yet)
4: $803000 is not used at this point
It may seem like alot of wasted memory but the AMIGA can only
AUTOCONFIG in 64K blocks.
The second half of the 'LS139 is used to convert the R/W signal
of the 680x0 to the read & write lines used by the NCR53C80.
Z4 -the 7406 will be used as the interrupt driver. I want to
use INT2* for the NCR's interrupts and INT6* for the DRQ*. DON'T
install the 7406 untill the real driver is available. Your AMIGA
won't like getting interrupted by the NCR53C80!
That is all there is to the SCSI interface. (Atleast for now)
It is possible to add DMA capibilities to the board but lets get the
thing up and running first!
READING THE "NET-LIST"
The schematic "AMSCSI" was made on an IBM XT using Future-Net software.
I wish that someone had a good schmatic capture pgm for the AMIGA !
Anyway to wire a board from the "net-list" ignore the "Path Ref" &
the "Symbol Ref" cols.
EXAMPLE: Part of the net-list
Signal Desc Path Ref Circuit Designator Symbol Ref Pin
IGNORE PART# IGNORE PIN #
1,(AS) (This is the signal name)
1-1 P1 (part #) 195 74 (pin)
1-1 Z1 191 1
1-1 Z5 196 6
1-1 P1 195 16
1-1 Z5 196 2
1-1 P1 195 14
1-1 Z5 196 3
The signal (AS) should be wired from pin 74 of P1 to Z1 pin 1 and
Z5 pin 6
The signal (C1) should be wired from pin 16 of P1 to Z5 pin 2
Continue this for the rest of the net list. EASY ISN'T IT.
It is recommended that the SCSI bus be terminated with 220 ohm / 330 ohm
resistors. These are not included on the "net-list". Every SCSI signal
should have a 220 ohm resistor to +5v, and a 330 ohm resistor to gnd.
You might want to try it without the terminators, but leave room for them
just to be safe..........
When I get a chance I will make a schematic on Dpaint.
I have included two BASIC programs that will help you test your board.
1: SCSIMon - a small monitor that constantly reads the NCR53C80
and desplays the reg.s in HEX
2: SCSIdvr - a very crude program that "PEEKS & POKES" the
SCSI . With it you can FORMAT, READ, & WRITE
a hard disk. It takes about 10-20 sec to read,
or write 1 sector !! ( Not blazing speed is it?)
I hope to have an assembly (source) language program in the near future.
It is called------- SCSI68K.asm
If anyone can help with the DRIVER, PLEASE, let me know!
I can be reached through AMIGA/INFO BBS @ (215) 430-3969
GOOD LUCK Rich Frantz