Need capture and signal help for homebrew accelerator project

[MacPlus2300]

Looking for a logic analyzer capture on a Macintosh Portable (or M5126 backlit) motherboard, PDS connector side. I’m scoping the bus timing for a homebrew accelerator project.


Signals needed, all captured simultaneously, PDS pins in parens:


• /AS (c8)


• /DTACK (b7)


• /DELAY.CS (a5)


• /EXT.DTACK (b30) probably idle/high in stock config, but capture it anyway


• 16M reference clock (b31), just as a timebase


Trigger on falling edge of /AS. Want to see: (1) how many 16M clock cycles between /AS falling and /DTACK falling on a normal RAM access, (2) whether /DELAY.CS ever asserts during a normal cycle or only under specific conditions (e.g. slow ROM/I-O access), and (3) confirmation that /EXT.DTACK is truly unused in stock config. A few captures; one during a plain RAM read, one during a ROM read, one during any I/O access (SCC/VIA) if you can trigger on those that would be huge. 8-16 channel analyzer is plenty, all this data would be extremely helpful and valuable to me if anyone has the capability to do this.

 

[Froggy814]

I only have a 4 channel logic analyzer. Would I be able to do it with that? And I don't quite know how to trigger ram rom or scc/via read If you could tell me how those would be triggered. I would be happy to help. I can help with a lot if you need.

 

[MacPlus2300]

Four channels should be fine, if you do a few passes.
Pass 1 (most useful): /AS (c8), /DTACK (b7), 16M clock (b31), /VPA (c5). Trigger on falling edge of /AS. /VPA tells us for free whether a given cycle was RAM/ROM vs SCC/VIA
Pass 2: swap /VPA for /SYS.RST (c30), same other three. Start capture right at power-on to catch boot-ROM timing specifically
Pass 3: /AS, /DELAY.CS (a5), /EXT.DTACK (b30), clock. Just want to know if these two ever actually assert during normal use.

For RAM vs ROM without decoding the address bus you can look for dominant activity in each such as power on capture for ROM heavy and desktop operations capturing RAM activity. If your software can trigger on /VPA falling instead of /AS, that’d isolate an SCC/VIA cycle directly. Even getting pass 1 I wrote here would be a huge help and a step in the right direction for my project!

 

[Froggy814]

Cool! I'll get a couple of videos for you made up when I can today.

EDIT:
I'll read three separate things.
Boot up: meaning when spacebar is pressed and the computer successfully boots into mac os.
Playing Oregon trail: you know what that means!
Inserting Floppy and formatting it or other. (not certain if my floppy drive works... I have cleaned it but it doesn't seem to be working correctly...)

 

[MacPlus2300]

Cool! I'll get a couple of videos for you made up when I can today.

EDIT:
I'll read three separate things.
Boot up: meaning when spacebar is pressed and the computer successfully boots into mac os.
Playing Oregon trail: you know what that means!
Inserting Floppy and formatting it or other. (not certain if my floppy drive works... I have cleaned it but it doesn't seem to be working correctly...)

That will help. Does your analyzer also export as a format? Like csv or another kind of file

 

[Froggy814]

It exports as a .csv, .wfm, and .bin! I hope i can figure out how it all works! I bought it very recently and am still learning the quircks!

 

[MacPlus2300]

That would be great to get either one of those files. I can send you the pinout of the PDS if you need for the passes.

 

[Froggy814]

Oh good! I have the pinout on hand... I printed it!