Quadra 700 - 68040 33mhz or 40mhz upgrade

[AlpineRaven]

Evening all, 

If I decided to swap the CPU over to 33mhz or 40mhz 68040 which I have them both, would it speed up at 33mhz or 40mhz without any other logicboard mods - I tried searching online and I cant find any info/pinpoint.

Such as, LC475 you can install 68040 33mhz but you have to change the resisters on the logicboard to get 33mhz to show.

Cheers

AP

 

[Dog Cow]

Evening all, 

If I decided to swap the CPU over to 33mhz or 40mhz 68040 which I have them both, would it speed up at 33mhz or 40mhz without any other logicboard mods

My best guess is that you'll need to modify the oscillator or some other related components on the motherboard to increase CPU frequency. Otherwise all you'll have is a CPU that's rated for 33 Mhz or 40 Mhz, but is still operated at stock 25 Mhz.

 

[trag]

What Dog Cow said.

Except for some microcontrollers and a few other oddballs, CPU have (a) pin(s) for one or more clock signals.  The incoming clock signal controls how fast the CPU operates.   Changing the CPU and not changing the clock signal just gives you a different CPU operating at the same speed.

There are all kinds of edge cases and exceptions.  And, of course, with slightly more modern CPUs the CPU operates at some configurable multiple of the incoming clock signal.    But for the 680x0 family, the above is accurate.

 

[Byrd]

Apparently the max you can clock chip a Quadra 700 is 37Mhz, which seems unlikely, more low 30's to ensure serial/sound etc continues to work.

http://lowendmac.com/2014/overclocking-the-mac-quadra-series/

JB

 

[Dog Cow]

Apparently the max you can clock chip a Quadra 700 is 37Mhz, which seems unlikely, more low 30's to ensure serial/sound etc continues to work.

http://lowendmac.com/2014/overclocking-the-mac-quadra-series/

And here is our answer: you have to replace the oscillator with one that operates at a higher frequency.

 

[jessenator]

Sorry for the necro post, figured I would continue to ask questions rather than start a duplicate thread.

Most of the sources linked, and additionally the OutputEnablers clock chipping kits, are related what is essentially overclocking the original 25MHz CPU, so my follow-up questions are:

• If one was to have both a true 40 MHz 040 and an appropriate 80 MHz crystal, would there be any operational issues on the machine? Do these same limitations apply? and to follow up:
  
• How is the bus speed of the machine set? is it clocked/timed by the 50MHz stock crystal, or is it more complicated than that, and the above solution wouldn't work?
  
• Is the 700 fairly hard-built to operate at a 25 MHz bus frequency, and would things like RAM and/or VRAM timing would be adversely effected?
  
• If this is even relevant at this point in the questions, are there board power considerations to pay attention to?
  

Thanks

 

[johnklos]

The motherboard has to be able to support the same speeds as the CPU in most instances. This is why the Quadra 700, which is older, can't quite go to 40 MHz or beyond - things stop working because the timings are too far off.

Whether an m68040 is marked as a 40 MHz part really doesn't matter. Except for super early m68040s (which are often labeled as engineering samples), all '040s are basically from the exact same fab processes. There was nothing different at all about the 40 MHz ones except that they were tested at 40 MHz and labeled. I've never seen a single m68040 that wouldn't run at 40 MHz.

Some Quadras have issues with their serial ports above certain speeds. From what I remember, the Quadra 700 simply won't run faster than 37 MHz or so, so I think it's more than just the serial ports. The memory and VRAM need to be faster, too, since the bus speed is based on the CPU speed.

Of course, running stuff faster requires more power, but unless your power supply needs recapping and/or is otherwise flakey, overclocking won't start taking so much power that the default power supply won't be able to handle it.

 

[jessenator]

The motherboard has to be able to support the same speeds as the CPU in most instances. This is why the Quadra 700, which is older, can't quite go to 40 MHz or beyond - things stop working because the timings are too far off.

That's what I was afraid of. So did Sonnet's QuadDoubler get around that limitation with some of their own trickery?

 

[johnklos]

That's what I was afraid of. So did Sonnet's QuadDoubler get around that limitation with some of their own trickery?

The QuadDoubler and other clock doublers basically run the m68040 at twice the clock speed when no bus activity is going on. Luckily the m68040's 4K cache made it possible to run stuff for little bits of time without accessing memory, so these were useful some times.

I've been meaning to benchmark a Quadra 630 set to run at 25 MHz with a QuadDoubler and the same machine without the QuadDoubler set to run at 40 MHz. I think in many kinds of work, 40 MHz will be faster.

 

[jessenator]

Well that's a bummer... 

Thanks for the info  

 

[johnklos]

Moving to 33 MHz is still completely doable, and is 133% of the stock speed.

Some folks on here are trying to make a new run of QuadDoubler-type boards. I wonder how far they've gotten...

 

[jessenator]

Moving to 33 MHz is still completely doable, and is 133% of the stock speed.

And, apologies if I seem thick, but based on the info you shared above regarding the 040 die, there's no benefit to swapping stamped CPUs, correct?

 

[johnklos]

And, apologies if I seem thick, but based on the info you shared above regarding the 040 die, there's no benefit to swapping stamped CPUs, correct?

There is no benefit, unless the CPU is a different mask.

If you want a more overclockable / cooler running m68040, you can get a later mask CPU, like the K63H or L88M, which is made on a .57 micron process, compared with the .8 micron of the m68040s made from 1989 through 1995 (except the E26A, which was .65).

 

[jessenator]

Well, we'll see what version I have when it gets here :lol:

It's not a Chinese seller, but a reputable stateside vendor, so it will be legit, just don't have a photo of the chip itself.

I should really have asked before I bought, but spilled milk and all that.

 

[Fizzbinn]

Some folks on here are trying to make a new run of QuadDoubler-type boards. I wonder how far they've gotten...

That would be awesome...  I lucked out finding an L88M 68040 a while back on ebay sold as "Motorola processor" that would love to run in one those.

 

[jessenator]

Hmm, looks like January 27 was the latest update, but promising. Human Malware (tm) is probably the biggest setback right now.

 

[jessenator]

If you want a more overclockable / cooler running m68040, you can get a later mask CPU, like the K63H or L88M, which is made on a .57 micron process, compared with the .8 micron of the m68040s made from 1989 through 1995 (except the E26A, which was .65).

So where does 02E42k fit in? That's the one I just got in the mail from Herb Johnson. From this site it looks like it's one of the .65um process, yeah? February '95? so a tiny bit better?

 

[Fizzbinn]

From info @johnklos posted in that thread:

Original XC68040s (D43B, D50D, D98D, E31F) run hot and are .8um masks, but will run fine at 33 MHz with a heat sink.

The E26A is an XC part with a .65um mask, which might be a little cooler.

Starting with the E42K mask, they are fully qualified MC68040 parts with .65um masks.

 

Then K63H reduced the mask to .57um.

 

Finally, the latest / last version is the L88M, which is also .57um, but runs cooler than the K63H according to some sources. This version is usually made by Freescale and has their logo in place of the Motorola M.

 

[jessenator]

Thanks for the link  well sounds like I made out fairly well then. I'll still keep the heatsink of course, for due diligence.