Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site ccivax.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxn!ihnp4!qantel!dual!lll-crg!seismo!rochester!ritcv!ccivax!rb From: rb@ccivax.UUCP (rex ballard) Newsgroups: net.micro,net.micro.atari Subject: Re: (FASI), SASI, SCSI - General info on SCSI (PLEASE READ) Message-ID: <297@ccivax.UUCP> Date: Fri, 4-Oct-85 20:04:41 EDT Article-I.D.: ccivax.297 Posted: Fri Oct 4 20:04:41 1985 Date-Received: Mon, 7-Oct-85 05:02:27 EDT References: <123@apr.UUCP> <279@ccivax.UUCP> <268@aum.UUCP> Organization: CCI Telephony Systems Group, Rochester NY Lines: 147 Xref: watmath net.micro:12255 net.micro.atari:1279 This came up in net.atari but affects ALL micro-computer owners, no matter what brand. > > Is the ST port really SASI? (Are we talking similar or are we talking ^^^^ > identical) In otherwords can I use a industry standard SASI controller > and Disk? This would be great. > -- > ------------------------------------------------------------------------------- > Erik James Freed > Aurora Systems > San Francisco, CA > {dual,ptsfa}!aum!freed SCSI is not the same as SASI. SCSI was based on SASI, but is much simpler to integrate. SCSI is to computers what RCA Phono Plugs are to stereo. The Atari DMA port is very close to SCSI, it provides all the critical interface signals for a "Kludge Box" which could be made by any company that wanted to do it. My guess is that Atari had a specific chip in mind, but I dont think the 5380 was the one they had in mind. SCSI is a very high speed genaric "flexable backplane". It is capable of handling up to 8 other SCSI controllers. Each SCSI controller can control up to 8 "logical devices", including R/W disks, Tape drives, WORM drives, CD-ROM drives, Printers of various types, and even other computers. Any combination of "Initiators" (computers/pc's...) and "Targets" (peripherals) may be combined. Each "logical device" may store/address up to 4 GIGABYTES of storage. Let's see, that's 64 devices, and (best case) about 256 GIGABYTES. Did someone say the Atari wasn't expandable (like me)? SASI uses separate Command data and DMA data busses, supports only 16 Megabytes/Logical device, and is primarilarily a "Winchester" controller only. Most SASI devices are available in SCSI, but many SCSI devices (CD-ROMS) may not be available in SASI. The Atari Port is VERY CLOSE to SCSI, but requires a little "glue" and an interface chip, such as the NCR 5380 series chips. To interface to the 538{5,1,0} you have to get three address lines to the address ports. Here is an example: [Note: this is from an earlier article - it looks about like what Ive seen, but I'm not sure] > Pin out of the ST Hard Disk Port. > > 1 - Data 0 2 - Data 1 Pins 11,13,15, and 17 Ground > 3 - Data 2 4 - Data 3 > 5 - Data 4 6 - Data 5 > 7 - Data 6 8 - Data 7 > > 10 - Interrupt Request (IRQ) > > 12 - Reset > > 14 - Acknowledge (DMA) (READY) > > 19 - Data Request (DMA) (DRQ) > > 16 - A1 (an address line) > 9 - Chip Select - the processor (not dma) has the data/A1 bus > 18 - Read/Write (Probably processor and DMA generated read/write signals) Latches can be used to get extra address lines from data for example: CS A1 RW 0 0 W trigger address latch 0 1 x pass this combination to the CS on the 5380 1 x x dma i/o essentially something like this: -------------------------------------------------------- |optional SCSI BUS | |parity data BSY SEL ATN ACK RST I/O C/D MSG REQ | ------------------------------------------------------- | |||||||| | | | | | | | | | ------------------------------------------------------- | 5380 | ------------------------------------------------------- |||||||| a0-2 ||| cs | dma data ------------- | |||||||| data bus |small latch| | ----------------| | | ------------- | | | !cs&(a1=0) !cs&a1=1 Add some software and you have instant expansion. I am not a hardware engineer and have no idea whether this would work, it is a guess based on documentation of the 5380 chip. Don't go groaning too loudly about the fact that they didn't do it "on board". They wanted to "keep the price down", a real SCSI port has 25 twisted pair balanced lines or 25 shielded ones. There are a few companies making SCSI interface chips which may be even more appropriate to the ST. Here are some manufacturers: Courtesy Mini/Micro Systems (Feb 1985, pg 125) Adaptec Advanced Micro Devices Data Technology Emulex Intel NCR Shugart SMS/OMTI Western Digital Xebec There is a good chance that at least one of these companies has a chip that is a perfect match for the ST. Would some people try looking at some spec sheets and post which come closest? A more complete chart is on pg 125 of that issue. Some good Articles include: Mini-Micro Systems May 1984 pg 241 Mini-Micro Systems Feb 1985 pg 123 Computer Design Nov 1983 pg 64 Electronic Design Oct 31,1984 pg 263 It is also known as ANSI PROPOSED STANDARD X3T9 BE CERTAIN THE DEVICE IS SCSI, AND NOT SASI, THEY ARE NOT THE SAME!!!!! There are SCSI to SASI adapters available along with SCSI to just about any standard you want. Basically all they do is demultiplex the DMA/ COMMAND channels. I haven't seen the Habba drive yet, is there an "SCSI OUT" port on it? By the way, there are kits to put SCSI on the MacIntosh (Xebec I believe). There are SCSI Adapter boards for most IBM compatibles (from almost anyone). Apple has announced plans to incorporate SCSI into the MAC (probably Jonathan). So if you want to be able to use an SCSI peripheral for IBM on an Atari you can. My guess is that when Peripheral manufacturers see that they can get the IBM, MacIntosh, Atari ST, and the Amiga market with the same product, "SCSI compatibility" will become more important than "IBM compatibility". Fortunately, SCSI compatibility is MUCH easier to accomplish.