TF536 + 68000 relocator and ROM board project.

[exxos]

Use a 22v10 then ? TOS104 why bother to decode it when glue does it, plus TF536 won't run with it anyway..

[stephen_usher]

Use a 22v10 then ? TOS104 why bother to decode it when glue does it, plus TF536 won't run with it anyway..

If I'm not using the ROM sockets then I have to do the decoding for TOS 1.x.

I know that the TF536 won't run it but this board will also have a 68000 on it, which you can switch to, and on that you may very well want to run TOS 1.xx. Also, someone may want to use the "TF536" socket/connector for something else other than a TF536 in future.

[stephen_usher]

OK, this GAL code should do the trick:

Code: Select all

Name     TOS 2.06 ROM decoder ;
PartNo   00 ;
Date     28/09/2020 ;
Revision 01 ;
Designer Engineer ;
Company  Personal ;
Assembly None ;
Location  ;
Device   g16v8 ;

/* *************** INPUT PINS *********************/
PIN  1   =  A18                       ; /*                                 */ 
PIN  2   =  A19                       ; /*                                 */ 
PIN  3   =  A20                       ; /*                                 */ 
PIN  4   =  A21                       ; /*                                 */ 
PIN  5   =  A22                       ; /*                                 */ 
PIN  6   =  A23                       ; /*                                 */ 
PIN  7   =  !ROM2                       ; /*                                 */ 
PIN  8   =  !AS                       ; /*                                 */ 
PIN  9   =  RW                       ; /*                                 */ 

/* *************** OUTPUT PINS *********************/
PIN  13   =  !ROE                       ; /*                                 */ 



SELECTED=RW & AS & !A18 & !A19 & !A20 & A21 & A22 & A23;

ROE=SELECTED | ROM2;

[stephen_usher]

I'm getting on with the schematics based upon @derkom 's CPU relocator Kicad project.

Well, here's my bit anyway (I couldn't make it any smaller and it being legible):

Schematic-part.jpeg (42.49 KiB) Viewed 3021 times

I just need to add the pin going into pin 20 of the lower ROM (/CE) which is driven by /ROM2.

Derkom, I do have an problem with your Kicad project, it can't find the footprint for the 74HCT157D chips. Also the jumpers aren't documented so I don't precisely know what they do.

So, now I have to try to remember how to define the PCB! I've done it once before, back in April/May but I've forgotten!

[stephen_usher]

I've a rough PCB layout now.

The dimensions are correct but the placement of the ROM pin is just a ball-park for the moment, but it gives a general idea.

The maximum dimensions are 20cm x 11cm.

PCB.jpg (83.76 KiB) Viewed 2993 times

I'm going to have to think about holes for screwing support feet as otherwise the board is not going to be stable.

[stephen_usher]

OK, I've worked out what all derkom's headers were for now... no need to bodge wires now!

[stephen_usher]

Almost there mechanically.

IMG_2041.jpg (92.46 KiB) Viewed 2946 times

[PhilC]

Looks good to me @stephen_usher

[stephen_usher]

PCB order placed with PCBway but I think I've hit the Autumn Lunar Festival so there's probably going to be a 2 week delay, so that'll be 3 weeks in total.

P.S. This is the final board.

PCB.jpg (183.99 KiB) Viewed 2915 times

P.S. Actually it's only a 5 day delay, so that's OK.

[derkom]

Derkom, I do have an problem with your Kicad project, it can't find the footprint for the 74HCT157D chips. Also the jumpers aren't documented so I don't precisely know what they do.

Sorry for late reply. It's been a really busy week.

I got the footprints from SnapEDA, who have footprints for almost everything. The specific page for these muxes is here.

The jumpers aren't jumpers, except the one labelled SW. SW is the switch for selecting which CPU is active. All the other pin headers on there are for sending the switched signals over to CPU1, because I didn't want that socket switched on the PCB, as I wanted to be able to plug in devices that required those signals regardless of switch state. So, the left hand 64-pin socket doesn't have anything switched, and the 68000 that I have stuck on the top of my stack has the switched pins bent out and connected to these jumpers.

This post explains it, and this one shows photographs of what I mean.

If you're designing a board that is just a switcher, and doesn't need to provide these signals to one socket regardless of switch position, then you should just switch these lines the same way on both sockets.


Edit:

OK, I've worked out what all derkom's headers were for now... no need to bodge wires now!

Oh.