Breaking the 36MB RAM limit on the LCIII

[Trash80toG4]

However, I do perceive Apple lying to dealers and customers as a huge problem back in the day, and many people blindly believed and trusted Apple.

Lying, hedging, shading the truth . . . that's SOP, be it in marketing, advertising or politics. The Apple "faithful" are in a league all their own to this day . . . Kool-Aide connoisseurs.

 

[johnklos]

On this LCIII I am recapping (today)…I have a short (perhaps) offtopic question.
Its possible to get it running at 33Mhz as I understand.

It's very simple, since it's just removing a resistor and installing it elsewhere:
LCIII (P450) Speedup

Does it matter what/which speed coprocessor is installed?
What model should I search for?

Because the fastest m68881 only ran at 25 MHz, I don't know if the m68881 would have issues being overclocked to 32 MHz. On the other hand, all m68882 except for early samples were binned from the same parts, and many of those parts ran fine at 50 MHz, so you shouldn't have any problem running any m68882 at 32 MHz.

 

[johnklos]

Well the boards work, I was going to assemble and sell a couple but my cheap source of DRAM IC's fell through and the next cheapest source is about £1 a chip so with 32 chips and assembly I would probably have to sell tham at £60-£70 each which I suspect is more than anyone would pay....

I was thinking about one of these for my LC III+ (that hosts http://elsie.zia.io, which is actually about my LC II), but £60-£70 would be a bit much.

What might be easier and cheaper would be using a 128 meg SIMM. It should be possible to use a few logic gates to make RAS3 and RAS4 also activate the SIMM, but at higher addresses. Wouldn't something like this work?

RAS1 logical and RAS3 -> SIMM RAS1
RAS2 logical and RAS4 -> SIMM RAS2
RAS3 logical and RAS4 -> SIMM A11

(if they're active low, then adjust for that)

So first 16 megs of first bank works as it would in a 32 meg SIMM, the same as with the first 16 megs of second bank.

The third 16 megs comes from first bank of SIMM at A11=1 for both RAS and CAS, or from 48 to 64 megs. The fourth 16 megs comes from the second bank of 64 megs, from 48 to 64 megs.

It'd require cutting / disconnecting SIMM RAS1 and SIMM RAS2, but otherwise a single quad 74LS08 should be all that's needed, no?

 

[Paralel]

Was the ROM limitation of the first rank size of 4 MB on the logic board ever defeated?

 

[max1zzz]

I was thinking about one of these for my LC III+ (that hosts http://elsie.zia.io, which is actually about my LC II), but £60-£70 would be a bit much.

What might be easier and cheaper would be using a 128 meg SIMM. It should be possible to use a few logic gates to make RAS3 and RAS4 also activate the SIMM, but at higher addresses. Wouldn't something like this work?

RAS1 logical and RAS3 -> SIMM RAS1
RAS2 logical and RAS4 -> SIMM RAS2
RAS3 logical and RAS4 -> SIMM A11

(if they're active low, then adjust for that)

So first 16 megs of first bank works as it would in a 32 meg SIMM, the same as with the first 16 megs of second bank.

The third 16 megs comes from first bank of SIMM at A11=1 for both RAS and CAS, or from 48 to 64 megs. The fourth 16 megs comes from the second bank of 64 megs, from 48 to 64 megs.

It'd require cutting / disconnecting SIMM RAS1 and SIMM RAS2, but otherwise a single quad 74LS08 should be all that's needed, no?

This is something I have actually considered doing, it should work as long as the timings for the RAS and address signals line up (Which logically they should) you'l need to invert the RAS signals for A11 as RAS is active low adn address lineas are active high

In short, it's defiantly worth a go!

 

[max1zzz]

Was the ROM limitation of the first rank size of 4 MB on the logic board ever defeated?

unfortunately not yet

 

[johnklos]

I've ordered some 74F02. It should be very simple: cut two traces, run four wires from the two traces coming and going, then run two more wires for RAS3 and RAS4, plus power and ground.

I won't be back to test it until later in the month, though.

 

[Sphere478]

Hello all!

I am very very very interested in doing this for my lc-550 performa.
I have for a long time wanted more than 36mb.

I would like to offer any help I can for the project. And beta testing. Let’s get this thing maxed out!

 

[Sphere478]

Any

I've ordered some 74F02. It should be very simple: cut two traces, run four wires from the two traces coming and going, then run two more wires for RAS3 and RAS4, plus power and ground.

I won't be back to test it until later in the month, though.

Any news?

 

[trag]

I still think converting the HP A2580 RAM module would be the easiest solution although @johnklos 's idea is probably about as simple. Makes me nervous splitting the address space like that, though it shouldn't...

I suspect the A2580 is a little cheaper than the HP D4290.

The A2580 are available on Ebay (USA) for less than $8 each from Memory Masters with free shipping.

@max1zzz Do you know anyone who's traveling US to UK? I have a few on hand I could send to you, but shipping internationally has gotten so expensive...

I don't have an LCIII board myself.

 

[Sphere478]

I still think converting the HP A2580 RAM module would be the easiest solution although @johnklos 's idea is probably about as simple. Makes me nervous splitting the address space like that, though it shouldn't...

I suspect the A2580 is a little cheaper than the HP D4290.

The A2580 are available on Ebay (USA) for less than $8 each from Memory Masters with free shipping.

@max1zzz Do you know anyone who's traveling US to UK? I have a few on hand I could send to you, but shipping internationally has gotten so expensive...

I don't have an LCIII board myself.

Tell me what to buy tell me what to solder and I’ll try it! I’m in usa

I want the absolute maximum possible ram in this unit

 

[Sphere478]

Tell me what to buy tell me what to solder and I’ll try it! I’m in usa

I want the absolute maximum possible ram in this unit

I can also make a PCB in kiCAD 6 if somebody wants to guide me about the details or upload a starting project

 

[Sphere478]

I ordered the larger module. The one you recommended.

I see the other one looks like a 16 chip config. Is that even compatible with what we are trying to do?

I do have some 128mb and 64mb sticks in my collection.

I worry about clearance on the large stick..?

 

[max1zzz]

@max1zzz Do you know anyone who's traveling US to UK? I have a few on hand I could send to you, but shipping internationally has gotten so expensive...

Afraid not though there isn't really much to test tbh, those simms should work with a couple of trace cuts and some jumpers ran (As they are essentially the same design as my simm from what I see just with the extra RAS's ran to the slot rather than a connector

I might give @johnklos's idea a go since I do have the parts to test that

@Sphere478 first thing you need to do is verify this is actually possible on the 550 - I don't have a 550 so haven't checked. Although the 550 uses a Sonora derived ASIC there is no grantee the extra RAS signals exist on the 550's ASIC. Start by looking at pins 95 and 98 on the ASIC and see if they are connected to anything, if they are not you need to measure them with a oscilloscope and see if you see the RAS signals there, if they are connected to something you need to look at what they are connected to, if like the LCIII the connecto to a resistior that than dosen't go anywhere thay proably are extra RAS signals, if they connecto to anything else they defiantly aren't

It's also entirely possible they the extra RAS signals exist on the 550's ASIC but on different pins, 95 and 98 are the pins on the LCIII's ASIC but there is no grantee that is where they are on the 550's (if they exist on it at all) if that's the case you'll just have to go round scoping all the unconnected pins looking for the RAS signals

In terms of height, I know my simms won't fit in a CCII (simmilar board to the 550) so I expect the HP simms will also have clearance problems as my SIMM couldn't really be made any shorter

 

[Sphere478]

Afraid not though there isn't really much to test tbh, those simms should work with a couple of trace cuts and some jumpers ran (As they are essentially the same design as my simm from what I see just with the extra RAS's ran to the slot rather than a connector

I might give @johnklos's idea a go since I do have the parts to test that

@Sphere478 first thing you need to do is verify this is actually possible on the 550 - I don't have a 550 so haven't checked. Although the 550 uses a Sonora derived ASIC there is no grantee the extra RAS signals exist on the 550's ASIC. Start by looking at pins 95 and 98 on the ASIC and see if they are connected to anything, if they are not you need to measure them with a oscilloscope and see if you see the RAS signals there, if they are connected to something you need to look at what they are connected to, if like the LCIII the connecto to a resistior that than dosen't go anywhere thay proably are extra RAS signals, if they connecto to anything else they defiantly aren't

It's also entirely possible they the extra RAS signals exist on the 550's ASIC but on different pins, 95 and 98 are the pins on the LCIII's ASIC but there is no grantee that is where they are on the 550's (if they exist on it at all) if that's the case you'll just have to go round scoping all the unconnected pins looking for the RAS signals

In terms of height, I know my simms won't fit in a CCII (simmilar board to the 550) so I expect the HP simms will also have clearance problems as my SIMM couldn't really be made any shorter

might be a little difficult for me to probe that board while running. I haven’t rigged up a way to power it outside the case. And the lc-550 case is rather cramped.

can I ohm between the chipset and the ram slot? Could you indicate the points? You are much more familiar with this than I‘ll do my best to catch up though

here are some high res of the patient.

 

[Sphere478]

Second

 

[Sphere478]

Okay! Got the stick in! It’s purdy!

but bad news…

it is too tall to use

is there a simm stacker that I could use to put it at a right angle?

 

[lilliputian]

There were a number of ram expander cards that let you re-use smaller ram simms in a single slot by combining them together. Check eBay, there were a number of them in various shapes and sizes, both branded and un-branded. Avoid MicroMac "SimmDoubler" cards, not because they're expensive on ebay (they are), but they do something a little different from most others.

 

[Sphere478]

pics

 

[Sphere478]

I’m not finding any that looks like they will fit. I may have to make one unless somebody else sees something out there?