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PostPosted: Sun Sep 13, 2020 6:29 pm 
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With respect to BDD's concern, the /OE of the EEPROM is tied to CPU pin 40. So shouldn't that mitigate the bus contention?

@Jeff, what should I look for to see if you concern has been handled?

@All, while trying to find parts on Mouser I noticed that the CY7C199CN is out of stock and obsolete. It looks like it will be hard. Not sure what to do about that, although I suppose I could use a regular width static RAM in an adapter.

Mousers results for the DS1813 contain a number of parts in the through hole format that differ slightly in part number. See
https://www.mouser.com/Search/Refine?Keyword=DS1813

Usually when this happens there's something I don't know about part ordering.


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PostPosted: Sun Sep 13, 2020 7:16 pm 
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Martin_H wrote:
With respect to BDD's concern, the /OE of the EEPROM is tied to CPU pin 40. So shouldn't that mitigate the bus contention?

That connection wouldn't make any sense. Pin 40 on both the 'C02 and '816 is RESETB.

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@All, while trying to find parts on Mouser I noticed that the CY7C199CN is out of stock and obsolete. It looks like it will be hard. Not sure what to do about that, although I suppose I could use a regular width static RAM in an adapter.

That SRAM continues to be available in SMT form. You would have to get or make an adapter that accepts SOIC28 and converts it to DIP28. Unfortunately, the entire industry is rapidly turning away from DIP, as it is no longer cost-competitive to mass produce new designs with it.

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Mousers results for the DS1813 contain a number of parts in the through hole format that differ slightly in part number...

I recommend Mouser SKUs 700-DS1813-10T&R or 700-DS1813-5T&R, in that order.

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PostPosted: Sun Sep 13, 2020 9:25 pm 
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Martin_H wrote:
With respect to BDD's concern, the /OE of the EEPROM is tied to CPU pin 40. So shouldn't that mitigate the bus contention?

@Jeff, what should I look for to see if you concern has been handled?
I read some of the preceding posts a little too hastily and I overlooked the fact the manufacturer says an '816 will work in this board. And that claim seems plausible, based on the schematic (from your link upthread). BDD's concern is satisfied because both of the memories' /OE are driven by an inverted copy of Phi2, and my concern is satisfied by the manufacturer's claim and by a superficial inspection of the glue logic.

-- Jeff


Attachments:
Apatco NCS-EB50 Schematic.jpg
Apatco NCS-EB50 Schematic.jpg [ 1.34 MiB | Viewed 302 times ]

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PostPosted: Sun Sep 13, 2020 9:36 pm 
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Something like the IDT 71256SA seems to be available from Mouser still , and 0.3" wide DIP


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PostPosted: Sun Sep 13, 2020 11:16 pm 
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@Dr Jefyll, thanks.

@BDD, I misread the schematic because it crossed across pin 40, but didn't have the dot. As Dr Jefyll, it continues to an inverter to Phi2.

@Martin A, thanks for the suggestion.


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PostPosted: Mon Sep 14, 2020 1:59 am 
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Dr Jefyll wrote:
Martin_H wrote:
With respect to BDD's concern, the /OE of the EEPROM is tied to CPU pin 40. So shouldn't that mitigate the bus contention?

@Jeff, what should I look for to see if you concern has been handled?
I read some of the preceding posts a little too hastily and I overlooked the fact the manufacturer says an '816 will work in this board. And that claim seems plausible, based on the schematic (from your link upthread). BDD's concern is satisfied because both of the memories' /OE are driven by an inverted copy of Phi2, and my concern is satisfied by the manufacturer's claim and by a superficial inspection of the glue logic.

-- Jeff

Hmmm...this is the first time I've seen a schematic.

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PostPosted: Mon Sep 14, 2020 3:59 pm 
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BigDumbDinosaur wrote:
Hmmm...this is the first time I've seen a schematic.

No worries. It was in the Google Drive folder link in the first post. I didn't upload it to the forum as given this was a commercial product, rather than forum member designed.


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