Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!husc6!ut-sally!pyramid!decwrl!sun!cmcmanis From: cmcmanis@sun.uucp (Chuck McManis) Newsgroups: net.micro.amiga Subject: Re: Sasquatch Print (sidecar flames) Message-ID: <6901@sun.uucp> Date: Thu, 4-Sep-86 14:53:00 EDT Article-I.D.: sun.6901 Posted: Thu Sep 4 14:53:00 1986 Date-Received: Fri, 5-Sep-86 03:20:44 EDT References: <225@plx.UUCP> <6802@sun.uucp> <277@pttesac.UUCP> Distribution: net Organization: Sun Microsystems, Inc. Lines: 87 This is a reference to Marnix A. van\ Ammers article <277@pttesac.UUCP> I am including at the end for reference but not up front since people always seem to misinterpret who sent what. Marnix et al, I was not the one dissapointed in the placement of the sidecar. And I would like to clarify some of the points I made in my original rebuttal to the person (I am sorry but I don't have the original and don't remmeber your name) who complained about the sidecar and the state of things in general. My three reasons that I speculated for Commodore not putting the side car on top were noise, timing relationships, and the FCC. On the first, a ribbon cable would generate quite a bit of noise, for a good treatise on the subject call up Byte by Byte in texas and talk to them about getting the Pal certified. (It uses the cable to the expansion unit on top approach. When they were showing it at a Badge meeting the connector appeared to be a machined housing that consisted of the outer shield box and an inner pc board that did the actual connecting. All things considered this seems like a reasonable way of doing things but it is expensive. [On a side note, while it is difficult and expensive for C/A to add a ribbon cable, no one is stopping you, the industrious hacker, from kluging up anything you want.] As for timing I did a paper design of a SCSI controller that would plug into the side of the Amiga and was quite shocked at how little margin there was for getting signals routed around. I found my self going from LS to ALS to F just to meet my performance goals. In two cases the margin for strobe to data valid was under 5 ns. If I wanted to design to that close a spec I had better make darn sure the lines between my board and the cpu were as clean and as fast as possible. Ribbon cable and 24 Ga wire in general doesn't seem to friendly to this. I grant you it is not impossible but it does add one more hindrance to reliable operation. Lastly, I brought up that venerable institution the FCC. (:-)) Due to a combination of factors they have simultaneously become more strict and slower in their processing. They have to approve all computing devices that go into the home. They measure them by their RF emissions. Try this experiment : Go get a 4 inch piece of ribbon cable and connect it to a connector. Then connect this assembly to your Amiga, then turn on your TV. See all that pretty snow? That is why the FCC wouldn't approve it. Now wrap that connector in foil and try to make the snow go away, not easy is it. It could be worse, you could use a 5" cable and find it was exactly 16 wavelengths long, (given the 7.14 Mhz signals) and really watch the noise fly. I guess I am trying to stress it is difficult and expensive and both of those would hinder the production I suspect. Those are my opinions we welcome your replies ... --Chuck >>>>>>>>>> original article follows <<<<<<<<<<<<<<<<<<<<<< > In article <6802@sun.uucp> cmcmanis@sun.uucp (Chuck McManis) writes: > >Three problems with putting the sidecar on top of the Amiga : > > o Noise (from the buss cable) > > o Timing ( every nanosecond counts on this bus) > > o FCC (unless you put the thing in a faraday box you would blast > > recption for miles) > > Sorry, I'm not an expert, but I don't buy any of those reasons. > I feel the same dissapointment as Chuck McManis does. I don't > have space to the side of my Amiga. The buss cable could be shielded. > It would only have to be about 4 inches long. I don't believe that > would screw up the timing (I understand that a signal propagates > more than 12 inches in a nano-second, so 4 inches would effect > timing by 1/3 nano-second or so -- can't be that critical -- > the CPU isn't going all *that* fast afterall). > > The FCC isn't going to care if the thing > sits on top, under, behind, or to the side. The FCC does care about > noise and like I said the bus cable could be shielded. > > I think the real reason is that they came up with the name, > then later realized they couldn't very well put a "side-car" > on top. That plus the few extra bucks it would > cost to have 4 inches of shielded cable (maybe $20 ?). > > OK all you engineers, go ahead and flame me about what > 4 inches can do. > > Marnix > -- > Marnix A. van\ Ammers > Home: (707) 644-9781 Work: (415) 545-8334 > {ihnp4|ptsfa}!pttesac!vanam CIS: 70027,70 -- --Chuck McManis uucp: {anywhere}!sun!cmcmanis BIX: cmcmanis ARPAnet: cmcmanis@sun.com These opinions are my own and no one elses, but you knew that didn't you.