Wanted: Advice on performing 68040 upgrade for Q605

[ojfd]

Hi guys,

Although we often mention Marc Schrier's page, we all should give a credit regarding this mod to that person from Japan, namely

Hiromasa Yamaoka

who was first to do such mod.

But I've always wondered why the straight resistor swap won't do the trick. Schrier's page says it doesn't work, but it also doesn't say that anyone ever tried it with the clock generator/buffer swap. It seems to bear more experimentation. One of these days...

There could be numerous reasons. Gazelle clock generator chip (Apple p/n 343S1135 -a) is not documented anywhere (anyone care to ask Apple's engineering department ;-) ), hence nobody really knows what's going on inside that chip. It might be that it can't generate "clean" 40MHz due to its internal limits. It might be that long traces + extra capacitance at 40MHz distorts signal waveform. Nobody knows... I have absolutely no motivation to poke around with my Tek TDS724 scope inside that poor Q605 trying to improve it or demistifying Gazelle chip's inhards . If it works with extra oscillator, why bother? Period.

The process is simpler than sourcing a MC88916, and simpler installing, too. Just get a 20 MHz oscillator, take the power for it from the 31.3344 MHz oscillator on the corner of the motherboard by the video connector, remove R93 from the backside (also close to the video connector), and run the 20 MHz oscillator's output to the inside pad where R93 used to be (by inside I mean towards the center).

"johnklos", _You can not make it work without the help of PLL chip in any way_! (PLL stands for Phase Locked Loop, check Google or Wiki how it works, in caseYou don't know.)

In all Quadras + IIVx this PLL works as Frequency doubler. That means, you put 12.5MHz in and out comes 25MHz. You put 20MHz in -> out comes 40MHz.

Now, if You read Motorola's MC88920 and MC88916 data sheets very carefully, you will see that:

1. MC88920 has been designed specifically for the 20 and 25Mhz 68040 microprocessors.

2. MC88916DW70 will work at max 35 MHz processor frequency and has been designed for faster than 25MHz processors.

3. MC88916DW80 will work at max 40 MHz processor frequency and also has been designed for faster than 25MHz processors.

If the manufacturer says what we should use, it would be good engineering practice to follow his recommendations. In our case we all should be using DW80 version, not even DW70!

Running 35 MHz part (DW70) @ 40 MHz is already 5 MHz too much, but running 25 MHz part at that frequency is living on the edge.

Regarding heatsinks on "real" 68040/40 - just look how its done in Q840 - full 68040@40MHz, regular pin-grid heatsink. DW80 PLL chip. And it keeps going.

ojfd

 

[johnklos]

"johnklos", _You can not make it work without the help of PLL chip in any way_! (PLL stands for Phase Locked Loop, check Google or Wiki how it works, in caseYou don't know.)In all Quadras + IIVx this PLL works as Frequency doubler. That means, you put 12.5MHz in and out comes 25MHz. You put 20MHz in -> out comes 40MHz.

I'm sorry, but how can you tell me that I can not make it work when I've been running at least one of my Quadra 605s at 40 MHz this way for a decade? That doesn't make any sense.

If the manufacturer says what we should use, it would be good engineering practice to follow his recommendations. In our case we all should be using DW80 version, not even DW70!
Running 35 MHz part (DW70) @ 40 MHz is already 5 MHz too much, but running 25 MHz part at that frequency is living on the edge.

If that were true, nobody would overclock since overclocking is almost always running parts faster than what the manufacturer says.

We're talking about a simple PLL clock driver, not a multiple-million-transistor device like a CPU. Also, the implementations and specifications are identical for both with the only exceptions being a recommended change in the anti-jitter resistor for applications below 40 MHz (20 MHz CPU) and the guaranteed minimum working frequency:

http://www.mac68k.org/files/MC88916.pdf

http://www.mac68k.org/files/MC88920.pdf

The added oscillator's output simply goes to pin 8 of the MC88920 which is disconnected because of the removal of R93. How is that not working with a PLL when we're precisely working with the MC88920?

 

[ojfd]

"johnklos", _You can not make it work without the help of PLL chip in any way_!In all Quadras + IIVx this PLL works as Frequency doubler. That means, you put 12.5MHz in and out comes 25MHz. You put 20MHz in -> out comes 40MHz.

I'm sorry, but how can you tell me that I can not make it work when I've been running at least one of my Quadra 605s at 40 MHz this way for a decade? That doesn't make any sense.

OK, if you're using 20 MHz oscillator in your mod, would you mind telling me where that 40 MHz signal for the processor comes from?

:-D

ojfd

 

[johnklos]

OK, if you're using 20 MHz oscillator in your mod, would you mind telling me where that 40 MHz signal for the processor comes from?
:-D

Well, apparently each MC88920 on every Quadra 605 motherboard I've tried will take 20 MHz in on the SYNC line and produce something close to 40 MHz. Granted, the speeds from each differ a little - Clockometer shows 38.something on a couple, the "cpu: delay factor 1593" line is a little different on each (1593 is from a 50 MHz m68040; a true 40 MHz is around 1280, and some of the 605s are in the low 1200s and high 1100s which would put the actual clock between 36 and 39 MHz).

The reason I brought this up is that most people are not capable of desoldering and resoldering surface mount chips, so if you can get most of the speed with a lot less risk, it's worth sharing.

On the other hand, I just bought a lot of seven MC88916DW70 on eBay, so if anyone would like one or two, email me - I'll sell them at cost ($4.50 USD plus shipping).

 

[trag]

1. MC88920 has been designed specifically for the 20 and 25Mhz 68040 microprocessors.

Yes, I noticed that when I reviewed the datasheets last week. However, folks seem to run at 20 - 25 MHz even after they've swapped in an 88916. There might be problems if the 88916 gets hot or otherwise loses margin, I imagine.

2. MC88916DW70 will work at max 35 MHz processor frequency and has been designed for faster than 25MHz processors.3. MC88916DW80 will work at max 40 MHz processor frequency and also has been designed for faster than 25MHz processors.

If the manufacturer says what we should use, it would be good engineering practice to follow his recommendations. In our case we all should be using DW80 version, not even DW70!

The 88916s I have on hand are the '80, but I got mine as samples from Freescale over ten years ago. I wish I had somehow gotten more now, as I only have two. Freescale sent the part to IDT who does not appear to offer it any more, or if they do, they sure don't make it easy to figure out on their web page. Maybe it's a Flash thing.

The easiest place to get the 88916 now, is probably from Marc Schrier. He still lists them for $20 on his Output Enablers website. Assuming that info is still valid, that may be the only remaining source short of ordering 50 of them them Arrow. The problem is that Marc lists the DW70, not the DW80, so while the DW80 would be better, teh DW70 is probably all that is realistically available.

I guess I should go add MC88916* to my list of Ebay searches...

 

[ojfd]

.. folks seem to run at 20 - 25 MHz even after they've swapped in an 88916. There might be problems if the 88916 gets hot or otherwise loses margin, I imagine.

I don't quite follow you.. are you saying that people swapped 88920 for 88916 and are wondering why their computers aren't working at 40 MHz or are you saying that they swapped 88920 for 88916, changed resistors to go to 33 MHZ, added 20 MHz oscillator to go to 40 MHZ and then backed back to 20 - 25 MHZ because their Q605's were unstable?

I wish I had somehow gotten more now, as I only have two.

What? Isn't that enough? How many Quadras are you going to overclock?

Cheers,

ojfd

 

[johnklos]

.. folks seem to run at 20 - 25 MHz even after they've swapped in an 88916. There might be problems if the 88916 gets hot or otherwise loses margin, I imagine.

I don't quite follow you.. are you saying that people swapped 88920 for 88916 and are wondering why their computers aren't working at 40 MHz or are you saying that they swapped 88920 for 88916, changed resistors to go to 33 MHZ, added 20 MHz oscillator to go to 40 MHZ and then backed back to 20 - 25 MHZ because their Q605's were unstable?

There are two clocking issues here; one is running everything on the motherboard at a different speed (33 or 40 MHz), which is why some people have problems with the speed of the video memory, and which is also why people don't just swap the resistors to give them 40 MHz. The memory on all the Q605s I've seen have always been 70ns, whereas 60ns SIMMs are pretty common. My guess is that if the motherboard memory were faster, the 40 MHz resistor change would work.

The second clocking issue is bypassing the motherboard speed settings and sending a separate clock signal to the MC88920 (what I mentioned before). The page which discussed this also recommended doing the resistor swap to 33 MHz, probably so that the memory will run a bit faster. In this case, an unhappy MC88920 might give a different clock rate (somewhere between 36 and 40 MHz), but I can't imagine even the most unhappy MC88920 giving 25 MHz.

So the question is whether anyone who has swapped their 88920 for an 88916 has done a proper resistor swap, or inserted a 20 MHz oscillator signal, or both, and if they have, that'd be VERY strange... Where did you hear about these cases?

 

[trag]

.. folks seem to run at 20 - 25 MHz even after they've swapped in an 88916. There might be problems if the 88916 gets hot or otherwise loses margin, I imagine.

I don't quite follow you.. are you saying that people swapped 88920 for 88916 and are wondering why their computers aren't working at 40 MHz or are you saying that they swapped 88920 for 88916, changed resistors to go to 33 MHZ, added 20 MHz oscillator to go to 40 MHZ and then backed back to 20 - 25 MHZ because their Q605's were unstable?

The datasheet says that the 88920 is for slower 20 - 25 MHz operating frequencies. And that the 88916 isn't suited for the slower speeds. However, when doing a careful modification, the first step is to remove the 88920 and install an 88916. Then retest to make sure the board still works. At that point, one is operating at 25 MHz and it works fine, even though it's not recommended with the 88916.

That is what I mean.

I wish I had somehow gotten more now, as I only have two.

What? Isn't that enough? How many Quadras are you going to overclock?

I have two Q605s. When I'm done, I'll have no 88916s in my parts supply.

Although I am happy to see John's offer. If only I can remember it when I eventually get back to this project. I've implemented a new rule for myself, where I buy nothing until the moment I'm ready to use it. No more, "I'll buy this. It will be useful in that project three years from now and might be hard to find then." That's how I ended up with a living room (soon to be attic) full of electronic crap....

 

[johnklos]

The datasheet says that the 88920 is for slower 20 - 25 MHz operating frequencies. And that the 88916 isn't suited for the slower speeds.

Just curious - where in the datasheet does it say that they're not suitable for slower speeds?

Although I am happy to see John's offer. If only I can remember it when I eventually get back to this project. I've implemented a new rule for myself, where I buy nothing until the moment I'm ready to use it. No more, "I'll buy this. It will be useful in that project three years from now and might be hard to find then." That's how I ended up with a living room (soon to be attic) full of electronic crap....

Ha ha ha... If only we all followed those rules... Then again, I don't know if my Diesel Chevette would be finished and running now if I didn't hoard parts over the years... and I finally got a latest-mask version of the MC68060 (71E41J) which is a .32 micron device (compared with the original, which is a .6 micron device), and if I hadn't kept around my CyberStorm Mark III until I found someone who could repair it, I wouldn't have a working 80 MHz m68060 system right now... So it all depends.

When I lived in NYC, I always had to prefer smaller machines to larger ones, and I suppose I've tried to keep that philosophy. But if only we didn't hoard everything, there'd be one less stereotype about us, I suppose.

These chips are small, so I'll keep them for when you need a few, trag.

 

[yuhong]

Yeah, like that's gonna happen. They are like $250-$300 each in bulk according to Freescales' site.

Well, they did eventually make a 40Mhz 68LC040, which is now at half that price, and as a bonus these has the FPU emulation bugs fixed.

 

[Bunsen]

now at half that price

Bargain! [)] ]'>

 

[yuhong]

Bargain!

Of course, that is for *without* the coprocessor.

 

[tecneeq]

There's another simpler way to get to 40 MHz which used to be available from here:http://gabezing.sytes.net/LC475-40Mhz-E.html

However, that site's been unavailable for a while and archive.org doesn't have copies. Does anyone have a copy or know of a mirror? We need to put those up.

Just wanted to add that the original Hack of the LC475 is magically available again. i guess sytes.net has removed their restrictive robots.txt, wich in turn led Archive.org to list the old sites as available again. Enjoy "Reach to Quadra840AV? LC475-40Mhz-Clockup" by Hiromasa Yamaoka:

http://web.archive.org/web/20040219005118/http://gabezing.sytes.net/LC475-40Mhz-E.html

 

[uniserver]

from the link above:

I changed MC88920 to MC88916DW80, and my LC475 is working at 42Mhz perfectly. Higher clock causes unuseable serial ports (Ummm---regrettable).

Wow 42mhz that is pretty bad-ass! !

I hate to sound non adventurous. I'm pretty happy with 33mhz OC!

from the sound of it, /w More work, I could drive that higher!

But then if i do this…. I will end up talking my self out of wanting a Quadra 840av. I want one !

 

[tecneeq]

Some LC475 run stable at 40MHz just as they are. Why not try it before you get a large 840av?

And when it works, treat yourself by getting a new 840av. ;D

 

[MinerAl]

But then if i do this…. I will end up talking my self out of wanting a Quadra 840av. I want one !

Yeah,but then you'll have to see how over clocked you can get the 840! 48? 50? 66?