bryce@COGSCI.BERKELEY.EDU (05/11/87)
::::::: Several different memory expansion boards all cause the same problem: ::::::: Streaks and missing bits start to show up on the screen. Sometimes entire objects like the resize and front/back gadgets become corrupted on all windows. It would seem that these boards, all which have their own memory controllers, are affecting CHIP memory. ::::::: The esiest way to crash these defective expansion products is to bring up a 'clock' window or two and let it sit for a few hours. The clock display will trash and eventually crash with an address error or illegal instruction trap. ::::::: What in the design of these boards is defective? Would any designer that has solved or avoided this problem like to comment on the technical aspects? :::::: B
spg@well.UUCP (05/16/87)
[line eater food............] In Article <8705110100.AA27374@cogsci.berkeley.edu> bryce@COGSCI.BERKELEY.EDU writes: <Several different memory expansion boards all cause the same problem: <Streaks and missing bits start to show up on the screen. Sometimes entire <objects like the resize and front/back gadgets become corrupted on all <windows. It would seem that these boards, all which have their own <memory controllers, are affecting CHIP memory. <The esiest way to crash these defective expansion products is to bring up <a 'clock' window or two and let it sit for a few hours. The clock display <will trash and eventually crash with an address error or illegal <instruction trap. <What in the design of these boards is defective? Would any designer that <has solved or avoided this problem like to comment on the technical <aspects? This problem could have a number of causes. It is possible that the memory board is malfunctioning in some way. However, it is more likely that the design of the memory is marginal. Since the expansion connector is DIRECTLY connected to the MC68000, the Amiga is very sensitive to the effects of noise and the expansion spec reccommends that ALL of the signal lines be buffered. The spec further states that the trace lengths should be kept as short a possible to reduce capacitive loading. The prototype of the Alegra was built on a wire-wrap board and exhibited the same types of crashes described above. I spent about a week and a half chasing this "ghost" and finally was convinced that the problem would be solved by the 4 layer pcb that we designed. We did a proto run of 5 boards and sure enough the flakiness was gone and the level of signal noise was significantly reduced. The moral of the story is that to design reliable expansion devices for the Amiga 1000, one should follow the spec and use good pcb design techniques. Don't forget lots of decoupling capacitors also. We used a 4 layer board, both for the increased noise immunity and to increase to odds of passing FCC. Steve Grant Engineering Manager Access Associates
phils@tekigm2.TEK.COM (Philip E Staub) (05/18/87)
In article <3077@well.UUCP> spg@well.UUCP (Stephen P. Grant) writes: >memory board is malfunctioning in some way. However, it is more likely >that the design of the memory is marginal. Since the expansion connector >is DIRECTLY connected to the MC68000, the Amiga is very sensitive >to the effects of noise and the expansion spec reccommends that ALL of >the signal lines be buffered. The spec further states that the trace >lengths should be kept as short a possible to reduce capacitive loading. It's suggestion/comment/question time. Does anyone think it feasible or desirable to develop an expansion connector plug in board which passes a buffered, self-powered (i.e., this board would have it's own power supply or a connector for an input from an external power supply) version of the expansion bus out the other side? Yes, yes, I know the standard answer: buy an expansion box. But I can't help but feel that there have to be people out there who bought (86 pin) bus expansion boards, thinking they would "never" have a need for any more than one or two plug in boards, then find themselves in a bind if they need three or four and can't get enough drive on the bus pins to make all the boards work at the same time. Or maybe there's already such a product. (If so,...........NEVER MIND 8-) ). Phil -- ------------------------------------------------------------------------------- Phil Staub tektronix!tekigm!phils (206) 253-5634 Tektronix, Inc., ISI Engineering P.O.Box 3500, M/S C1-904, Vancouver, Washington 98668
spg@well.UUCP (Stephen P. Grant) (05/23/87)
kigm2.TEK.COM> Sender: Reply-To: spg@well.UUCP (Stephen P. Grant) Followup-To: Distribution: Organization: Whole Earth 'Lectronic Link, Sausalito, CA Keywords: In article <1776@tekigm2.TEK.COM> phils@tekigm2.TEK.COM (Philip E Staub) writes: >It's suggestion/comment/question time. Does anyone think it feasible or >desirable to develop an expansion connector plug in board which passes a >buffered, self-powered (i.e., this board would have it's own power supply or >a connector for an input from an external power supply) version of the >expansion bus out the other side? > >Yes, yes, I know the standard answer: buy an expansion box. But I can't help >but feel that there have to be people out there who bought (86 pin) bus >expansion boards, thinking they would "never" have a need for any more >than one or two plug in boards, then find themselves in a bind if they >need three or four and can't get enough drive on the bus pins to make all >the boards work at the same time. The standard answer is an expansion chassis OR a properly designed buss passthru. It is certainly feasible to design and build a "buffer" card complete with power supply, but it makes little sense economically. This buffer card is essentially a "Zorro" interface without the slots. It would have to buffer ALL of the signals on the 86 pin connector with transceivers (74F245s). It would need to provide buss steering logic. It should have a power supply that provides +5 volts and probably +12 and -12 volts. Add in a good printed circuit board, a few connectors, capacitors, a case for the whole thing, and FCC approval and what you have is an expansion device with no expansion that will have to sell at the retail level for $100 to $200 or more. Would you be willing to pay for this? I submit that few people will. >Or maybe there's already such a product. (If so,...........NEVER MIND 8-) ). > >Phil Earlier this year, Cltd and Microbotics where supposed to be working on this type of product to fix the problems that they created by not buffering the buss on their implementations of a passthru. Since then, nothing seems to have come of it. Why? Because they probably found that it was impossible to do economically especially when you consider that there are at most 150K Amiga 1000s in the world and little hope for more. Stephen P. Grant Engineering Manager Access Associates
phils@tekigm2.TEK.COM (Philip E Staub) (05/24/87)
In article <3117@well.UUCP> spg@well.UUCP (Stephen P. Grant) writes: >In article <1776@tekigm2.TEK.COM> phils@tekigm2.TEK.COM (Philip E Staub) > writes: >> >>Yes, yes, I know the standard answer: buy an expansion box. But I can't help >>but feel that there have to be people out there who bought (86 pin) bus >>expansion boards, thinking they would "never" have a need for any more >>than one or two plug in boards, then find themselves in a bind if they >>need three or four and can't get enough drive on the bus pins to make all >>the boards work at the same time. > >The standard answer is an expansion chassis OR a properly designed buss >passthru. It is certainly feasible to design and build a "buffer" card >complete with power supply, but it makes little sense economically. >This buffer card is essentially a "Zorro" interface without the slots. >It would have to buffer ALL of the signals on the 86 pin connector with >transceivers (74F245s). It would need to provide buss steering logic. >It should have a power supply that provides +5 volts and probably +12 >and -12 volts. Add in a good printed circuit board, a few connectors, >capacitors, a case for the whole thing, and FCC approval and what you >have is an expansion device with no expansion that will have to sell at >the retail level for $100 to $200 or more. Would you be willing to pay >for this? I submit that few people will. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > Sorry, Stephen, but I think that we'll have to agree to disagree on this one. Take an early Amiga owner who has spent an extra $500 or so to add an extra meg of memory outboard. Now that there are some larger outboard (expansion bus) memories available, he wants to add another board. At this point, it is my understanding that, even if the first board passed the bus, he's taking a chance to add another board. As I see it his options are limited: 1) Take the risk of being able to run both boards at the same time. 2) Sell his old memory board, probably for a healthy loss, so he can put a new larger one on the expansion bus by itself. 3) Sell the old board and sink a kilobuck into an expansion chassis. I know, the chassis itself doesn't cost $1000, but by the time you've bought the chassis and replaced the 1meg of ram, *and* factored in the loss on the old 1 meg board, I'd say you're going to be in that range. Presumably, one would not have done all this without some additional expansion (like the additional memory I mentioned above) in mind, so we're talking a significant incremental investment to gain a marginal increase in (let's say) ram size. I'd be the first to admit that I'm not that close to the current pricing of expansion products for the Amiga (I can't even think about expanding mine until I get it paid off 8-( ), but my perception is that these days you can get a 2 meg ram board for about $400 regardless of bus flavor. Enter the bus buffer product: let's use your $200 figure for a price tag. Now, it's going to cost $200 plus the new ram board (let's figure $400 for that). You wind up with a meg more ram than you would have had if you had bought the expansion chassis. Maybe I'm way off base here, but the way I see it, that's a savings of a *minimum* of $400 over the expansion chassis route. Now maybe $400 doesn't mean as much to you as it does to me, but that represents a significant incentive in my book. Is it just me, or do I see the markings of the "disposable society" here, in that the implication is that you must discard something that is still perfectly usable in order to expand? This may be acceptable to a business user, but for a little guy like me who has to fund his own recreational computing, it definitely is out of the question. (Note: this is another reason that I haven't expanded my Amiga. Right now I can't justify the cost of an expansion box, nor am I willing to believe that just one expansion bus plug in will be all I'll ever want.) >Earlier this year, Cltd and Microbotics where supposed to be working on >this type of product to fix the problems that they created by not buffering >the buss on their implementations of a passthru. Since then, nothing >seems to have come of it. Why? Because they probably found that it >was impossible to do economically especially when you consider that there >are at most 150K Amiga 1000s in the world and little hope for more. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ I, for one certainly hope you're wrong here. I think that if I had it to do all over again, even if presented with the choice between the 1000 and the 2000 I would probably still buy the 1000, because of both price and styling/esthetics (I like the keyboard garage, and I definitely *don't* like the keyboard and mouse plugged into the front of the box). If my vote counts for anything (are ya listening C-A) I say "keep the 1000 around". Also, isn't the A500 supposed to have the same expansion bus connector? Sorry this got so long winded, but you made a few comments I just couldn't let go unanswered. Phil -- ------------------------------------------------------------------------------- Phil Staub tektronix!tekigm2!phils (206) 253-5634 Tektronix, Inc., ISI Engineering P.O.Box 3500, M/S C1-904, Vancouver, Washington 98668