System 80 X-4020 Expander KiCAD woes

CheshireNoir · 20-02-2023, 02:38 PM

Hey Folks,
I've put the X-4020 Expander into KiCAD, but it's revealed a number of problems I'll need to resolve. IF anyone has a real X-4020 open and a multimeter, could I get you to check a few things for me?

The first one is pretty simple: Is pin 5 of X36 (74LS16) connected to pin 9 of Z46 or pin 5 of Z47? (That particular Hex inverter appears in two different locations on the board :-D )

Cheers!

John

CheshireNoir · (This post was last modified: 20-02-2023, 06:57 PM by CheshireNoir.)

Some more questions:
(Hoping some one knows this peripheral well enough to be able to answer)
Where is the global label "37E8 RD" supposed to connect to? It comes from Z34 on pin 5 but I can't "see" the other end. I suspect one of the labels connected to Z38 or Z39 are wrong...
On the 50 pin S100 bus connector, What are CLOCK and FX supposed to connect to? Are they just disconnected?

Cheers!

John

(PS. If anyone wants a copy of this early document, just let me know and I'll send it to you)

***ChickenMan*** · 21-02-2023, 12:14 AM

Will open mine up tomorrow afternoon once home and see what I can find for you.

CheshireNoir · 21-02-2023, 11:03 AM

(21-02-2023, 12:14 AM)ChickenMan Wrote: Will open mine up tomorrow afternoon once home and see what I can find for you.

That would be legendary! There's no rush on this. It's going to take me months to get to my next step.
I've already started my "redesign" using a 32K SRAM to replace the 4116 RAM. After that I'll need to investigate using something to replace the 1771. That'll simplify the power delivery a lot :-)

Cheers!

John

***ChickenMan*** · 21-02-2023, 07:45 PM

Well I opened up my Exp Unit. These is no screen print to identify what chip is what, nothing. There are 2 x 74LS16 chips and so many via's that I'm having trouble following any path. The Schematics shows LS16 (36) P5 going straight to a P9 74LS74 but using my multimeter neither P5 of the LS16's appear connected to the LS74. Would photo's of the top & bottom of the board help ?

CheshireNoir · 21-02-2023, 08:21 PM

Thanks Chickenman,
It'd definitely be better than nothing! I suspect I'll be able to trace it as the masks are pretty good.
Cheers again!

John

***ChickenMan*** · 21-02-2023, 09:32 PM

The pics I took of top and bottom of my X-4020 expansion unit are way too big to post here, and to reduce them in size means a reduction in quality. So have put them in the Repository in the Vintage/System-80/Documentation/Pictures folder.

EDIT: Also added CheshireNoir's chip annotated version.

CheshireNoir · 22-02-2023, 12:36 AM

Sir you are a legend!

John

RedskullDC · (This post was last modified: 22-02-2023, 01:54 AM by RedskullDC.)

Hi John,

That sounds really cool.

I'd recommend a WD1772 (or 1773) FDC, it will be the easiest to use in a 28pin DIP package, with on-board digital data separator.

Will limit you to using double density only, and make you incompatible with all the single density operating systems though.
May need to tweak the boot code in the ROM too(?).

Most of the Double Density Model 1 DOSes out there all had a single density track #0, as the DD adapters all (well mostly all) had
both the 1771 and 1791 chips on board, each of which was selected by a soft switch. Normally, the 1771 was selected on power-up or reset.

Not too difficult to create an *all* double density disk though.
Example: Newdos/80 V2 has support for either a single or double density track #0 through it's PDRIVE commands.

1771 isn't too hard to find, as there were a few alternate manufacturers apart from WD (National Semi for example: https://www.ebay.com.au/itm/224738121982).

Cheers,
Leslie

CheshireNoir · 22-02-2023, 11:22 AM

Cheers RedskullDC.
If I can find a 1771 variant that doesn't need +12V and -5V, then I'll stick with that. I was looking at the 1770, which seems to have a single density toggle.
(That's a long way down the road tho. Wanna get the RAM plumbed in first.)

John