Designing a portable RAM card

[techknight]

Adding one select line at a time, added bank switching A20 line. 

Now I am seeing up to 5MB so far, NICE... I will keep doing this for each 1MB block at a time until I figure out where my issue was. 

 

[techknight]

I found the problem. Not the solution yet... 

Soon as I tie in the last MB of RAM, to take it up to 9MB is when it goes haywire. I'm thinking its running into ROM somehow. odd... As long as I stay at 8MB and under, it all works beautifully. 

Soon as I add the last MB, spectacular failures

My original CPLD design is perfect. Just didnt like the last MB. 

 

[techknight]

Nevermind. I am an idiot. I had to re-read the notes, I can only go to 8MB. Not 9MB..

So my card actually works perfectly. I just tried to expand it past limits. 

 

[aplmak]

Techknight.. from what I recall they could only go up to a certain size depending on the model.. I think the limit was 9 on one of them.. the other 8MB.. I remember seeing this.. Perhaps this is why my PDS was missing the last chip so it only had 8MB total.. and that was a card from a 5120.. I wish i could remember.. but the max was 8MB on one and 9 on the other..

 

[aplmak]

This is also including the 1MB of onboard memory of course…. so 7MB on one card for one model and 8MB total for the other.

 

[aplmak]

YOU DID IT!!!!! HORRAY!!!!!

 

[aplmak]

So can you add the last chip for a total of 8MB on the card and make a jumper depending on the model??? So you can flip between 7MB and 8MB.. Get the order forms ready.. LOL!!!!

 

[techknight]

There... All good now. Its awesome, you can actually watch the diagnostic LEDs switch between banks as the mac starts up and tests RAM. 

 

[techknight]

No jumper needed. its right at 8MB. I just turned off the last MB, so it stays at 8MB instead of 9MB. So basically we are wasting half of the last chip. doing nothing. 

I could remap it in the expansion ROM area, but then we would need a special driver to tell the Mac OS to use it as RAM. 

The last thing I need to do is toss it in a Backlit model and see if it works. In theory, it should be universal. I actually did NOT need the DTACK connection on the non-backlit. So, we will see on the Backlit whether I need it or not. 

 

[aplmak]

So I think the 5120 can go up to 8MB MAX but the 5126 can take a total of 9MB...

 

[techknight]

I dont know. depends on where ROM is. if ROM is sitting at &H900000, then its stuck at 8MB as well. 

 

[aplmak]

Found this...

NAME  

MACINTOSH Portable M5126

MANUFACTURER  

Apple

TYPE  

Portable Computer

ORIGIN  

U.S.A.

YEAR  

1990

END OF PRODUCTION 

1991

BUILT IN LANGUAGE 

None

KEYBOARD  

Typewriter style, 80-key with numeric keypad

CPU  

Low power version of Motorola 68000

SPEED  

16 MHz

RAM  

1 MB (up to 9 MB)

ROM  

256 KB

GRAPHIC MODES 

640 x 400

COLORS  

Monochrome

SOUND  

8-bit stereo

SIZE / WEIGHT 

33.8 x 37.7 x 10.3 cm / 7.1 kg

I/O PORTS 

Serial, Parallel, SCSI, ADBx2

BUILT IN MEDIA 

One 3.5'' FDD 40 MB HDD (optional)

OS  

MAC OS 6.0.4 to 7.5.5

POWER SUPPLY 

Internal lead-acid battery 6.5V

PRICE  

$4200

 

[aplmak]

So 5120 can only go to 8MB total and 5126 to 9MB total.. You are testing on a 5120.. You should test on a 5126 board and bring it up… Perhaps my 5126 board.. heeee….

 

[techknight]

That means I need two different CPLD firmwares. One for backlit, one for not...

Maybe the next PCB i need to add a jumper to enable/disable the 9th MB. 

On my machine, that 9th MB will overlap ROM and she falls flat on its ass. lol.

I only ordered 5 PCBs on the first run to make sure I didnt have any hardware bugs. And I didnt, as I figured i wouldnt. I looked over that thing time and time again proofreading it. 

New PCB will have the jumper. I need to see if the fab house has solder paste stencils. that will make things so much easier and faster. I did my first board all by hand. 

 

[aplmak]

I'm sure everyone is cool with just getting 8MB's… I just thought there might be a way to just use that little extra ram… Yeah next design throw a jumper scenario on it if possible to flip back and forth..

 

[techknight]

According to the Backlit developer note, it has an 8MB ceiling as well... 

 

[aplmak]

You did a freakin awesome job!!!!!!!

 

[uniserver]

good job dude!

 

[Paralel]

The plot thickens, the Service Source also says there is a 9 MB ceiling:

http://tim.id.au/laptops/apple/legacy/macintosh_portable.pdf

 

[techknight]

Well, I know for a fact that the M5120 I have here on my desk, ROM starts at &H900000 which is the 9Megabyte marker. So yea I cant go past 9MB. 

Unless I add the last MB of RAM to the ROM Expansion address location, but that would require a special extension to tell System 6/7 to use that as RAM. That is something I dont know how to do.