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Rob Blessin Black Hole
Site Admin


Joined: 05 Sep 2006
Posts: 597
Location: Ft. Collins, Colorado

PostPosted: Tue Feb 07, 2017 9:40 pm    Post subject: Reply with quote

SlateBlue wrote:
Thanks, Rob. Have those rollers held up well over the years? Seems I read somewhere that the rubber has a tendency to deteriorate with age.
ive kept them stored in heated storage ,its the best I can do !
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Rob Blessin President computerpowwow ebay sales@blackholeinc.com http://www.blackholeinc.com
303-741-9998 Serving the NeXT Community since 2/9/93
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cubist



Joined: 20 Sep 2007
Posts: 246
Location: Cambridge, MA

PostPosted: Thu Feb 09, 2017 9:55 pm    Post subject: DSP memory Reply with quote

Would love to get some better front and back images of the DSP memory. Say from a scanner...
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SlateBlue



Joined: 23 Aug 2015
Posts: 75

PostPosted: Thu Apr 13, 2017 9:09 am    Post subject: Reply with quote

I've been trying to figure out how I can get the DSP module x-rayed so that the community can reproduce it. My brother-in-law is a vet, but he won't waste his time and resources on this hobby. You guys have any other ideas? I'm guessing there is a lack of schematics, otherwise this chip could be recreated?
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pentium



Joined: 23 Jun 2006
Posts: 1148
Location: Kamloops, BC

PostPosted: Thu Apr 13, 2017 6:36 pm    Post subject: Re: DSP memory Reply with quote

cubist wrote:
Would love to get some better front and back images of the DSP memory. Say from a scanner...


I photo enhanced a photo from the DSP project a number of years ago




The rest of my efforts are stored here.
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-NeXT 68040 Cube with NS 3.3 and 64Mb ram
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SlateBlue



Joined: 23 Aug 2015
Posts: 75

PostPosted: Thu Apr 13, 2017 7:25 pm    Post subject: Reply with quote

I'm no electronics guru, but since I have a physical module, wouldn't I be able to tone out all the connections with a multimeter? I assume it would be cumbersome, but doable.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Fri Apr 14, 2017 6:36 am    Post subject: Reply with quote

You probably could. Use the connectivity check function and try to avoid sending current through the chips. There is starting material here: http://www.nextcomputers.org/NeXTfiles/Projects/DSP_Expansion_Ram/
I used this http://www.nextcomputers.org/NeXTfiles/Projects/DSP_Expansion_Ram/SFSU_NeXT_DSP_Expansion_Memory.pdf (this design is for a larger DSP memory - 256 K x 8 ) as a basis.

It's always good to work based on a hypothesis and deduct as much as possible just from the traces. Here is what I see:

The design should be straight forward. The pins of the SIMM module are counted from the indent from 1 to 64. 1 to 36 are the 24 data lines from the bus with Vcc supply lines and ground lines in between. The SRAM chips are 8 bit wide so their data lines are directly mapped across the bus data lines (i.e. the lowest data lines to the chip on the left, the next one's the one in the middle, ...).

37 - 56 are the 16 address lines of the bus again with Vcc and ground lines in between. The 14 lowest should go directly to the 14 address lines of the SRAMs.

The highest lines starting with 57 are interesting and they will probably go together with the other logic chip (a 4 line 2 input multiplexer).

57 - DSPXY - an additional address line?! - we do not need it
58 - DSPRD - signals a read - goes to output enable of the SRAMs
59 - DSPWR - signals a write - goes to write enable of the SRAMs
60 - DSPRMEM - chip enable - goes to chip enable of the SRAMs
62 - DSPPS - chip enable - dito?!
63 - SRAMCS - some chip select - following the traces it seems to go to chip enable of the middle SRAM and somewhere else (it splits)

58, 59 and 60 might be inverted before going to the SRAMs.
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SlateBlue



Joined: 23 Aug 2015
Posts: 75

PostPosted: Fri Apr 14, 2017 1:18 pm    Post subject: Reply with quote

You're saying that putting current through a chip by way of a continuity test may damage the chip? I'm not sure how I would avoid this. I don't want to risk damaging the module.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Fri Apr 14, 2017 1:31 pm    Post subject: Reply with quote

Yes, the test current or voltage may harm chips.

Work your way forward step by step from the SIMM's 64 contacts and do not measure across chips, i.e. do not put the multimeter's leads on two pins of a chip.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Fri Apr 14, 2017 2:05 pm    Post subject: Reply with quote

I went a bit through some info on the DSP56001:

http://www.nxp.com/assets/documents/data/en/data-sheets/DSP56001.pdf
http://simson.net/ref/NeXT/byte/dsp.htm
http://uploads.cq-dx.ru/pdf/DSP/DSP56001UM2.PDF (uuuh Russia...)
http://cache.freescale.com/files/dsp/doc/inactive/DSP56001A.pdf

It seems to me that the DSP needs so called X and Y data memory to be present and maybe also program memory. So the DSPXY line would be used and DSPPS / DS as well.

As I said it would be good to find out how the pins 57 to 64 are wired.
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SlateBlue



Joined: 23 Aug 2015
Posts: 75

PostPosted: Fri Apr 14, 2017 7:32 pm    Post subject: Reply with quote

When I get some time, I'll read through that documentation and see if I can add anything useful.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Sat Apr 15, 2017 5:02 am    Post subject: Reply with quote

You will not get much information from these docs for the task of understanding the wiring diagram of the SIMMs module. We could start with a Google spreadsheet in which we work on the SIMMs wiring.

BTW, sometimes you can see through the module if you hold it up to a strong light source. If the module has a complete Vcc or ground plane than you would not see much, though.
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SlateBlue



Joined: 23 Aug 2015
Posts: 75

PostPosted: Sat Apr 15, 2017 12:53 pm    Post subject: Reply with quote

I took several photos of the module with it held near a fluorescent lamp. I'm guessing this module is composed of at least four layers? Anyway: link to Imgur album. You're correct, bobo68, there isn't much to be seen.
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bobo68



Joined: 03 Jun 2015
Posts: 194
Location: Germany

PostPosted: Sat Apr 15, 2017 1:05 pm    Post subject: Reply with quote

I guess it is 4 layers because there is a nearly continuous ground (or Vcc?) layer and then at least one internal layer for traces. More layers would be unusual for such a simple thing as a RAM module.

Ok, how shall we proceed?
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SlateBlue



Joined: 23 Aug 2015
Posts: 75

PostPosted: Sat Apr 15, 2017 1:18 pm    Post subject: Reply with quote

I'm probably going to need some guidance here. I have downloaded the documentation for the F158 mux in order to see the pinout. Do you have documentation of the memory chips? It may or may not help me understand how some of this goes together. If you want to create a spreadsheet and share it with me (Google Docs?) I can fill in what the continuity test tells me. This board has many vias, those vias appear to connect to some internal traces and I can't see where they go. It would appear to me that the ground plane exists on the side opposite of where the components are mounted. So, I then assume the Vcc plane exists on the component side. Thus, ground pins would be on the backside of the module, and Vcc pins would be on the front. Is this correct?

Again, I am no electronics guru, but I can learn. So, if my questions are a bit elementary, be patient as I'm just simply trying to grasp understanding.
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SlateBlue



Joined: 23 Aug 2015
Posts: 75

PostPosted: Sat Apr 15, 2017 1:49 pm    Post subject: Reply with quote

Documents for both the F158 mux and memory chips: here.
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