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Designing a portable RAM card

Replacing the RAM IC fixed it. So out of a handful from trag, only one was bad. Turns out I did not need DTACK so ill omit that in the next PCB revision.

Thats pretty good.

BTW. I only ordered 5 PCBs to make sure it all worked. First come first served.

Your looking at $75 per board for one without the LEDs. Or $80 if you want the LEDs for the cool factor.

I need to know how many are interested and qty so I can order all the correct parts.

 
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Hmmm. That's a 1 out of 9 failure rate on the chips so far. That's not so good. I hope you just happened across the bad apple and that's not typical.

Have you tried running something like NewerTech's RAMometer memory test (also available in Guages) or some of the memory tests in TechToolPro? Check the chips bitwise...

Fabulously excellent work.

Hmmm, browsed the thread again, rereading your progress.

I also suggest you test RAM performance (RAMometer will give you a MB/S tested indicator) with and without your DTACK wire connected. Is it possible that without DTACK, the CPU is timing out and assuming the data is on the bus at some point, but that with DTACK, the transaction might complete several cycles sooner?

If there's some logical reason why the above paragraph is misdirected, feel free to ignore it. :)

 
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DTACK is generated automatically by the GLU. So i dont need to worry about it. The backlit portable has no wait states. So the speed is literally as fast as the RAM access time. 

The non-backlit has wait states, I present the data available instantly, but the machine can only accept it within a certain amount of wait-states. 

Its hard to say why the chip was bad. I could have killed it for all i know. I dont have any ESD matting or anything. 

Also, do you have a link to any of those utilities? 

 
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This is sooooo awesome!!!!! And especially awesome of Techknight makes a 68020 to drop in it!!! Everyone will be in portable heaven.. Here is a song that I thought when it came out was awesome… Makes me think of my macs… lol!!!

 
Now thats odd. 

I got 9MB on haplains board, at the shop with my portable HDD. 

Since I dont have an HDD solution yet on my non-backlit portable at home, I am booting off a 6.0.7 disk tools disk. Well same thing. Memory manager error and address error when using 9MB.... 

Do you have to have a full install of 6.0.7? or a system enabler I am not aware of? 

 
Not to mention the bus incompatibilities. 68000 is a 16bit cpu with 16bit bus while 020+ is 32bit. So how do you run a 32 bit proc on a 16 bit bus? Im sure designers figured all this out 20+ years ago. But I havent.
Click to expand...
The Mac LC should be your inspiration because this is exactly what Apple did with it: The LC has a 16-bit bus and it's running a '020. 

On the PC side of the fence Intel released the 386SX which was the low cost version of the 386DX.  The 386DX had a full 32-bit external bus and the 386SX had a 16-bit external bus and fewer pins.  The actual core of the two chips were effectively the same.  (In the 1980s and early 1990s it was a lot more expensive to make a 32-bit system because your bus had to have many more traces.)  I know that for Intel, they solved the problem by using 2 clock cycles to load a complete instruction.  That is, every other clock cycle would either be the "high 16" or the "low 16."  

Since the '020 doesn't have a shorter bus variant I do wonder how Apple made it work.  At least we know it is possible to do.

 
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I am not going to say what techknight has done in the past as far as High-Tech electronics.  SW / HW

I'm sure this portable card wasn't no big thing for him :)

 
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Jumping the gun a bit here, but, if these sell very fast, and you run out of SRAM chips, Mouser has this chip (263 in stock):

http://www.mouser.com/ProductDetail/Alliance-Memory/AS6C1616-55TIN/?qs=sGAEpiMZZMt9mBA6nIyysDfDw0vDQxSw%2fJdd2EqgHt0%3d

It would be about $7 each if you bought 100 of them, but they have the same pinout as the TC55BVM416, are TTL compatible and are in the same package. Probably bump the cost of the card up from $75 to $100, but at least you'd be able to make more of them using the same PCB.

The only issue I see is that the AS6C1616 does not support X8 mode. Only 1M X 16. I'm still not clear on whether you're using the TC55BVM416 in 1M X 16 mode or in pairs as 2M X 8.

 
unrelated. 

I need someone with good internet digging skills. 

Looking for a motorola application note on the 68020. 

Motorola AN944

BTW, they are only going to sell as fast as I can make them. lol. 

 
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