Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site oakhill.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!ut-sally!oakhill!brianw From: brianw@oakhill.UUCP (Brian Wolf) Newsgroups: net.micro,net.micro.atari Subject: Re: (FASI), SASI, SCSI - General info on SCSI (PLEASE READ) Message-ID: <553@oakhill.UUCP> Date: Mon, 7-Oct-85 15:21:14 EDT Article-I.D.: oakhill.553 Posted: Mon Oct 7 15:21:14 1985 Date-Received: Wed, 9-Oct-85 06:27:00 EDT References: <123@apr.UUCP> <279@ccivax.UUCP> <268@aum.UUCP>, <297@ccivax.UUCP> Organization: Motorola Inc. Austin, Tx Lines: 224 Xref: linus net.micro:11049 net.micro.atari:1229 I would like to correct some misnomers presented in the following article concerning the relationships of the so called "FASI" and SASI/SCSI interfaces. >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 > The ST port is not SASI/SCSI compatible so one can not buy an industry standard SASI/SCSI product and directly attatch it to the Atari port, however it appears that a host adaptor can be built off the port that will let the Atari talk SASI/SCSI. Ofcourse somebody will have to write device drivers for the Atari operating system. >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. While it is true SCSI is not the same as SASI there is very little difference between the two. SCSI uses the same physical data and control bus as SASI with the exception of the ATN signal added to help make SCSI multi-hostable. SASI is a defacto standard that allows one host computer to talk to upto 8 controllers while SCSI is a "soon to be" ANSI standard that allows any combination of upto 8 host computers and/or controllers to talk on the same bus. Additionally SCSI has the ability to send data synchronously up to 4 Megabytes/sec. SCSI is much more intelligent than SASI and tends to off load many of the time consuming functions (mostly disk format operations) from the host computer. >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. The Atari DMA port is just that - a DMA port - and nothing more. Its only resemblence to SASI/SCSI is the REQ/ACK handshake lines and the 8 data lines. >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)? Basicaly true except that it is a combination of 8 host computers and/or controllers on the same bus rather than one host and 8 controllers as the above paragraph states. >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. SASI has only one data bus used to transfer both commands and data. Message and status information is also transferred over the same data bus. I am hopeful that all new products, including CD-ROMs, will be SCSI compatible. >The Atari Port is VERY CLOSE to SCSI, but requires a little "glue" >and an interface chip, such as the NCR 5380 series chips. I disagree. The Atari Port is nothing more than a DMA channel. The circuit shown below is a SCSI Host Adapter for the Atari. It might work. >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!!!!! This is not true. A SCSI controller will work as well in a SASI bus environment as will a SASI controller in a SCSI bus environment. The protocol for the physical aspect of both busses allows for this. Now it is true that the firmware aspect of SASI is different from the SCSI but only in terms of the command implementation. For example both SASI and SCSI send commands over the data bus in 6 byte command blocks (SCSI also has 10 and 12 byte command blocks which allow for a 32 bit logical block address and a 16 bit transfer length). SASI commands are designed to work on a track by track basis while SCSI is designed to work on the whole unit. For instance SASI has a format track command while SCSI has a format unit command. The basic operations such as read and write data are identical. What all this boils down to is the device drivers for SASI are slightly different from the device drivers for SCSI. >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 have never seen such a device. I think you mean host to SASI/SCSI adapters such as the NCR 5380. The same device is easily implemented using a simple circuit based on parallel ports. >I haven't seen the Habba drive yet, is there an "SCSI OUT" port on it? I believe that in the next year you will be seeing a number of high capacity drives with SCSI imbedded on the drive - therefore removing the added cost of a controller board. I am also happy to announce Motorola is building a single-chip controller which talks SCSI on one side and ST506, ST412, ESDI Serial, and ESDI Step disk interfaces. For more information see the cover story in the OCT. 3 issue of Electronic Design. >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. I agree - SCSI is a great interface and would be a boon for the types of machines listed. --------------------------------------------------------------------------- Brian D. Wolf Motorola MCU Division William Cannon at US 290 West Austin, Texas ---------------------------------------------------------------------------