137 lines
6.3 KiB
Plaintext
137 lines
6.3 KiB
Plaintext
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SCSI CONTROLLER
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This is a very preliminary doc. for a SCSI interface for the AMIGA.
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I know that it is fragmented, but I am trying to get something together
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quickly. Feel free to send me your comments.
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At the present time this design does not support DMA or AUTOCONFIG'ing.
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The "net-list" also includes parts for an optional 2 meg. memory add-on.
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At this time the memory does not work! I have to check my equations and
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analize that section of the board. The memory section does NOT upset the
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AMIGA or the SCSI interface. There are no special considerations when
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building the board. It runs off of the AMIGA's power supply and plugs
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into the EXPANSION PORT .
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The board uses 1 special part: NCR53C80 (sorry about that.)
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I used it because it handles most of the SCSI interface, and eliminates
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alot of "LS" chips. (The NCR53C80 is the CMOS version of the SCSI
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controller used by APPLE and most other venders!)
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Building the board
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WARNING ! This board plugs into the expansion port! That port is directly
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connected to the CPU and other chips in your AMIGA. Care must be taken so
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as not to short anything to +5v or gnd as that may DESTROY your AMIGA.
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The circuit and design concepts are sound, but YOU are in control of
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your machines destiny. This project is NOT for the casual hacker.
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REMEMBER, Don't yell at me if you break your machine!!!
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On the lighter side, my board worked the first time it was turned on.
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It must be easy if I didn't make any errors... Just take your time and all
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will be OK !
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After deciding where to locate all of the parts, use the "net-list" to
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wire it. I suggest doing all of the wiring to the board before installing
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the IC's. Remember that the NCR53C80 is sensitive to static, so be careful.
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Also before installing IC's it is a good practice to check the power and
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gruond pins on all chip sockets.
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PARTS LIST
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PART# LOC USE
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74LS688 ....................... Z1 ......... ADDRESS DECODER
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74LS139 ....................... Z2 ......... ADDRESS & R/W DECODER
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NCR53C80 ...................... Z3 ......... SCSI INTERFACE
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7406 .......................... Z4 ......... INTERRUPT BUFFER
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74LS244 .................... Z6 Z7 Z8 ...... MEMORY ADD. MUX
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PAL20RA10 ..................... Z5 ......... MEMORY CTRL PAL
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AMIGA CONNECTOR ............... P1 ......... 86 PIN
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SCSI CONNECTOR ................ P2 ......... 50 PIN
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MEMORY CONNECTOR .............. P3 ......... 60 PIN
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NOTE: DO NOT INSTALL U4,U5,U6,U7,U8 AT THIS TIME.
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If you want to wire it, go ahead the DRAM will be comming soon!
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CIRCUIT DESCRIPTION
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The reason for the 74LS688 (8 bit comparitor) is to allow for upgrading
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the board for AUTOCONFIG'ing. I don't plan to do this until I get the
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important work done (DRAM & CLOCK). It is not hard to use this way,
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you have to "install" the board anyway. The advantage of AUTOCONFIG
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is that the AMIGA decides where in the memory the board resides.
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This is not a problem since it is the only board in the system.....
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The PAL (Z5) is used to control the DRAM. It is not needed at this point
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so don"t worry about it.
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The 'LS139 is used to decode addresses intofour 16K blocks.
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1: $800000 is the NCR53C80
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2: $801000 is the PSEUDO DMA
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3: $802000 is for the CLOCK (not done yet)
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4: $803000 is not used at this point
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It may seem like alot of wasted memory but the AMIGA can only
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AUTOCONFIG in 64K blocks.
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The second half of the 'LS139 is used to convert the R/W signal
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of the 680x0 to the read & write lines used by the NCR53C80.
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Z4 -the 7406 will be used as the interrupt driver. I want to
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use INT2* for the NCR's interrupts and INT6* for the DRQ*. DON'T
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install the 7406 untill the real driver is available. Your AMIGA
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won't like getting interrupted by the NCR53C80!
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That is all there is to the SCSI interface. (Atleast for now)
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It is possible to add DMA capibilities to the board but lets get the
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thing up and running first!
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READING THE "NET-LIST"
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The schematic "AMSCSI" was made on an IBM XT using Future-Net software.
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I wish that someone had a good schmatic capture pgm for the AMIGA !
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Anyway to wire a board from the "net-list" ignore the "Path Ref" &
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the "Symbol Ref" cols.
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EXAMPLE: Part of the net-list
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Signal Desc Path Ref Circuit Designator Symbol Ref Pin
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--------------------------------------------------------------------------------
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IGNORE PART# IGNORE PIN #
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THIS THIS
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COL. COL.
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1,(AS) (This is the signal name)
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1-1 P1 (part #) 195 74 (pin)
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1-1 Z1 191 1
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1-1 Z5 196 6
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1,(C1)
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1-1 P1 195 16
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1-1 Z5 196 2
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1,(C3)
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1-1 P1 195 14
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1-1 Z5 196 3
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The signal (AS) should be wired from pin 74 of P1 to Z1 pin 1 and
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Z5 pin 6
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The signal (C1) should be wired from pin 16 of P1 to Z5 pin 2
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Continue this for the rest of the net list. EASY ISN'T IT.
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It is recommended that the SCSI bus be terminated with 220 ohm / 330 ohm
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resistors. These are not included on the "net-list". Every SCSI signal
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should have a 220 ohm resistor to +5v, and a 330 ohm resistor to gnd.
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You might want to try it without the terminators, but leave room for them
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just to be safe..........
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When I get a chance I will make a schematic on Dpaint.
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I have included two BASIC programs that will help you test your board.
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1: SCSIMon - a small monitor that constantly reads the NCR53C80
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and desplays the reg.s in HEX
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2: SCSIdvr - a very crude program that "PEEKS & POKES" the
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SCSI . With it you can FORMAT, READ, & WRITE
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a hard disk. It takes about 10-20 sec to read,
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or write 1 sector !! ( Not blazing speed is it?)
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I hope to have an assembly (source) language program in the near future.
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It is called------- SCSI68K.asm
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If anyone can help with the DRIVER, PLEASE, let me know!
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I can be reached through AMIGA/INFO BBS @ (215) 430-3969
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GOOD LUCK Rich Frantz
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