weber@brand.UUCP (Allan G. Weber) (03/13/86)
Some months ago I put together the MacSCSI hard disk interface from Fastime using a Xebec S1410 and a Seagate ST-506 5mb disk. It has worked reasonable well off my 512k Mac. When I got a Mac+ I wanted to get the S1410/ST-506 combo working off the Mac+ SCSI port, hopefully as a bootable device. I made a cable to go from the DB-25 SCSI connector on the back of my Mac+ to the 50 pin Berg-type connector on my Xebec controller board. Upon trying it out, the Mac+ never seemed to notice the disk on the SCSI port. It would never access it, either for booting or after booting from a floppy. Today I called Xebec to see if they knew how to get their S1410 to work off the Mac+ and they said that the S1410 definitly won't work on the Mac+. They said the S1410 is SASI while the Mac+ is SCSI and they are not compatible due to something Apple has done in their SCSI implementation. This surprised me since the Mac+ SCSI port uses the same NCR SCSI chip for the interface as does my Fastime MacSCSI board. Apparently Apple has done enough things differently in their SCSI implementation to make the port incompatible with SASI controllers, at least when using the SCSI support available in the Mac+ ROMs. I would be interested in hearing from anybody who can confirm all this. Right now I have a S1410 and a S1410A controller at home that are looking pretty useless. Allan Weber Univ. of So. Calif. Arpanet: Weber%Brand@USC-ECL Usenet: ...sdcrdcf!oberon!brand!weber
rick@ut-ngp.UUCP (03/15/86)
> ... >Today I called Xebec to see if they knew how to get their S1410 to work off >the Mac+ and they said that the S1410 definitly won't work on the Mac+. >... Well, I have gotten my S1410/Shugart combination working on my Mac Plus. I am using the SCSI manager to talk to the drive. So its not all that incompatible. However, there are problems. Apple decided that their SCSI interface needed no termination. This is probably contrary to the SCSI spec, but I haven't really checked. They could build it into the external cable except that they don't provide terminator power. The Apple schematic has a note that reads to the effect that the Mac power supply doesn't have enough current leftover to provide SCSI terminator power. This could be true if you hang 7 SCSI devices off the back of the Mac Plus. I would be interested in knowing how 3rd party companies have solved this problem. The S1410 controller also has no termination or pullups on SOME of the control signals. Look at your S1410 manual to see which. My solution was to build an external cable that provides standard SCSI termination for the 9 SCSI control signals and plug it into the end of the cable nearest the MacPlus. I run terminator power all the way down the cable from the S1410. I originally ran it out of the Mac, which did work, but didn't want to have to hack another Mac I wanted to connect to. This was sufficient to get the hardware interface to work. For longer cable runs (I have an 8 foot cable), you might also need to terminate the data signals. You could probably even just get away with simple pullups on the control signals that are not pulled up on the S1410 end of things. So, the termination is like this: +5 | / \ 220 ohms / \ | +--- signal | / \ 330 ohms / \ | gnd for each of the following signals; pin numbers are for the Apple DB-25: 1 REQ* 2 MSG* 3 IO* 4 RST* 5 ACK* 6 BSY* 15 CD* 17 ATN* 19 SEL* I built this by clamping a male and a female DB25 connector onto a short piece of 25 wide ribbon cable. I then peeled back wires from the ribbon cable to attach to a socket that has a 220/330 ohm resistor pack in it. You could, of course, also just use individual resistors. It looks pretty weird, but it works. You may just want to build all of this into your DB25 to 50-pin berg adapter cable. The +5 terminator power runs down pin 26 (I think) on the 50-pin cable. You have to add a wire on the S1410 controller to do this. For software, you can use the Apple Generic SCSI installer if you have a Shugart 5mb drive (or similar setup). It ran on my test setup with no mods and produced a volume that is bootable by the Plus. I have also subsequently modified my own driver to use the SCSI manager calls, and written my own installer. The installer code is pretty much a copy of the Apple code. The SCSI manager is documented in the December Software Supplement, that just recently shipped. Sorry, I cannot post the Apple Generic SCSI installer. It comes with the SCSI developer's package and is copyright by Apple. Maybe someone from Apple can comment on how to get this stuff from Apple. Also, since much of my current driver code was derived from the copyrighted Fastime software, I can't post it either. I have been working on a complete from-scratch public domain version, but I don't have time or motivation to finish it right now. You could probably also get the Fastime driver to work, bypassing the SCSI manager completely, but I was never successful in doing this. I quit trying when I got the SCSI manager to work. My final comment is that unless you enjoy hacking the hardware and driver software (I do) you should just buy off the shelf hard drives. I have heard from too many people from all over net-land that haven't either haven't gotten thier homade setups to work, or have setups that aren't all that reliable. At this time, you have to provide the hardware and software support yourself. On the other hand, I now have a system at home running on a 512K Mac with the Fastime board, and a system at work running off the Mac Plus. Both are very reliable, and I have learned a lot about the Mac in working on this project. If you really scavenge, you can do it inexpensively. My total hardware cost for a 5 mb system for the Plus ran about $250. (By the way, go for bigger drives, 5 mb is not enough. I already had some 5 mb drives.) Rick Watson University of Texas Computation Center arpa: rick@ngp.UTEXAS.EDU rick@ngp.ARPA uucp: ...seismo!ut-sally!ut-ngp!rick rick@ut-ngp.UUCP bitnet: ccaw001@utadnx phone: 512/471-3241