Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!usc!elroy.jpl.nasa.gov!lll-winken!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.hardware Subject: Re: 2320 on an A500 and external drive port hardware interfacing Message-ID: <16481@cbmvax.commodore.com> Date: 12 Dec 90 16:13:31 GMT References: <9012120327.AA16486@yoda.eecs.wsu.edu> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 83 In article <9012120327.AA16486@yoda.eecs.wsu.edu> gheller@YODA.EECS.WSU.EDU (Geoffrey Heller - CS216) writes: >Hello C= and other hardware hackers out there! Here are a few questions >which have been puzzling me for some time... >Question #1: > I have an A500 with Trumpcard 500 on it. I am very interested in the >2320 graphics board but I'm told it is only available for the A2000. Now, >I do have a bit of experience at hardware hacking and I would like to know >if it would be easy to add a 2320 onto my A500 bus. The A2320 (or any such device) doesn't sit on the system bus, it glomps on to the video bus generated by Agnus and Denise. To physically hook this to your A500, you would have to find a way to run the 12 digital video pixel bits from Denise, the syncs from Agnus, and a couple of power supply lines up to the A2320. Assuming it doesn't use -5V (which isn't on the A500), it might work, though it would be a rather ugly mess of wires, and you would have to figure out how to internally mount the thing. And you may very likely get into power supply loading problems on the A500. Scott Hood could tell you more about that. >If not, would anyone care to recommend a solution to the flicker problem on >A500's? The main problem with frame converting an A500 display is that you can't easily get to all 12 bits of digital video. An internal device can jumper over to them somehow, but anything external would have to use the analog RBG lines and run them through video ADCs before frame buffering. That's going to cost more than the digital solutions used in the A2000 and A3000. >Question #2: > I am currently working on a device which will utilize the Amiga external >3.5" disk port. In the AMIGA HARDWARE REFERENCE MANUAL (p311) it says, >"Each device must provide a 1000-Ohm pull-up resistor on those outputs >driven by open-collector devices on the Amiga." This seems to indicate that >I need to use a 1K pull-up on all OC's I use. But if you had four devices >daisy-chained in a row which used the same pin, that would mean that you >would have four 1K pull-up resistors in parallel on that line. Is this >supposed to happen? With four devices, that's 250 ohms per line. Not a big problem for your typical open collector buffer. They would probably work, like SCSI, if you only terminated the endpoints of the floppy lines, but I imagine the 1K value was chosen to handle 1 to 4 devices, each with their own termination/ pullup resistors. >Question #3: > If I choose not to use certain input and output lines on my device, can >I simply not connect those pins? If you're not providing passthrough, and your lines aren't too long, it'll probably work OK. It wouldn't hurt at all to provide pullups, though, for the shared lines you're not using. >I plan to read and write all used disk port lines (including the MFM >read and write) through a 74HCT244 buffer -- is this ok? You can buffer inputs to your device with a 74HCT244, but you can't drive the floppy bus with that one, it's not an open collector or open drain device. A common 7407 chip gives you 6 non-inverting open collector buffers in a 14 pin package, a bargain at twice the price. >Question #4: > When the sytem checks the drives using the "identification mode," the >system will receive 0000 0000 0000 0000 "no drive present" from my device. >Will disk polling continue after the system detects "no drive present?" >Specificly, if my device is connected to the Amiga external disk port and >a standard 3.5" drive is daisy-chained from it, will the Amiga automaticly >be able to use that external drive or not? The Amiga will look at each of the four floppy channels independently, so if your device doesn't identify itself as a floppy, but the next one does, the next one will get added automatically. Much like what normally happens in the A2000 with one internal and one external floppy -- unit 0 is automatic, unit 1 (second internal drive) isn't there, but unit 2 gets added as an external anyway. >- Geoffrey Heller gheller@luke.eecs.wsu.edu -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "I can't drive 55" -Sammy Hagar