LC III & LC 520/550 PDS slot compatibility

[jasa1063]

Is the PDS slot in a LC III electrically compatible with the PDS slot in a LC 520/550? I am look at getting an accelerator for my LC III and it is listed for a LC 520/LC 550.

Thanks!

 

[Melkhior]

Yes, the devnote for the 520 says it's the same. Page 30:

The expansion slot in the Macintosh LC 520 computer is an extended processor-direct slot
that accepts either of two types of PDS cards: the 96-pin PDS card used in the
Macintosh LC II computer or the 114-pin PDS card used in the Macintosh LC III. The
114-pin connector provides additional signals to support features of the MC68030
microprocessor that are not available with the 96-pin card.

 

[jasa1063]

Yes, the devnote for the 520 says it's the same. Page 30:

Thanks, that is what I thought, but just wanted to make sure.

 

[jasa1063]

This is the Interware 30-LC5250F accelerator I am getting. I am rolling the dice that it works and is compatible. We shall find out.

 

[zigzagjoe]

I've been wondering if someone would pick that up.

It is a close cousin to the SE/30 design I recently cloned, which means it runs at a multiple of the LB clock. Presumably 2x, for 50mhz in a system that was originally 25mhz. If your system clock is 33mhz, this card will not work. I think the guy was assuming that 30-LC5250F means for 520 and 550, however, the last 50 is the accelerator CPU MHZ rather than model and F refers to the presence of the FPU.

I'll be curious if booting from a floppy works with this accelerator, the SE/30 design had special logic to deal with that but it looks like the analogous GAL for this card is not present. Possibly not needed.

 

[jasa1063]

I've been wondering if someone would pick that up.

It is a close cousin to the SE/30 design I recently cloned, which means it runs at a multiple of the LB clock. Presumably 2x, for 50mhz in a system that was originally 25mhz. If your system clock is 33mhz, this card will not work. I think the guy was assuming that 30-LC5250F means for 520 and 550, however, the last 50 is the accelerator CPU MHZ rather than model and F refers to the presence of the FPU.

I'll be curious if booting from a floppy works with this accelerator, the SE/30 design had special logic to deal with that but it looks like the analogous GAL for this card is not present. Possibly not needed.

My LC III is running at 33Mhz, but I have access to 25MHz model I gave to a friend and we can just do a swap of the motherboards. It should all be good. Thanks for the info!

 

[Nixontheknight]

My LC III is running at 33Mhz, but I have access to 25MHz model I gave to a friend and we can just do a swap of the motherboards. It should all be good. Thanks for the info!

I actually overclocked mine to 33MHz. I wonder if an overclocked LC III runs a bit slower than one that's stock 33MHz

 

[jasa1063]

I actually overclocked mine to 33MHz. I wonder if an overclocked LC III runs a bit slower than one that's stock 33MHz

It should have the exact same performance as 33MHz LC III/Performa 460. The only difference is the clock speed and the fact it has a 33MHz 68030 on the motherboard.

 

[jasa1063]

I got the Interware Booster 30-LC52550F and it works with my 25MHz LC III. The interesting thing is the 68882 is only clocked to 33MHz and not 50MHz. This seems to be the case on some accelerators. My MicroMac Thunder LC is 33MHz for the 68030, but only 16MHz for the 68882 and my MicroMac Diimo 030 for my SE/30 is 50MHz for 68030, but only 25MHz for the 68882.

 

[zigzagjoe]

I got the Interware Booster 30-LC52550F and it works with my 25MHz LC III. The interesting thing is the 68882 is only clocked to 33MHz and not 50MHz. This seems to be the case on some accelerators. My MicroMac Thunder LC is 33MHz for the 68030, but only 16MHz for the 68882 and my MicroMac Diimo 030 for my SE/30 is 50MHz for 68030, but only 25MHz for the 68882.

How did you determine the clock speed of the 68882?

Fun fact about the SE/30 Diimo - there's nothing precluding full-speed operation if the FPU is of an appropriate rating. I run my FPU at 58mhz on my clone.

 

[Phipli]

I got the Interware Booster 30-LC52550F and it works with my 25MHz LC III. The interesting thing is the 68882 is only clocked to 33MHz and not 50MHz. This seems to be the case on some accelerators. My MicroMac Thunder LC is 33MHz for the 68030, but only 16MHz for the 68882 and my MicroMac Diimo 030 for my SE/30 is 50MHz for 68030, but only 25MHz for the 68882.

Do you have a photo of the card? Sometimes it is possible to easily increase the FPU speed. Some boards have a jumper, others have a socketted clock. Some FPUs labelled as 33MHz run happily at 40 or even 50MHz

 

[jasa1063]

Do you have a photo of the card? Sometimes it is possible to easily increase the FPU speed. Some boards have a jumper, others have a socketted clock. Some FPUs labelled as 33MHz run happily at 40 or even 50MHz

Pictures of the accelerator is are in Post #4 in this thread.

 

[Phipli]

Pictures of the accelerator is are in Post #4 in this thread.

So you have a 50MHz part running at 33MHz?

As @zigzagjoe mentioned, how did you measure this? It seems wasteful of a high performance FPU.

 

[jasa1063]

So you have a 50MHz part running at 33MHz?

As @zigzagjoe mentioned, how did you measure this? It seems wasteful of a high performance FPU.

Using PowerDemo from Daystar shows the 68030 @50MHz and the 68882 @33MHz. The SpeedOMeter 3.23 results confirm the FPU score is indeed running at 33MHz. The Performance Test result is 35 whereas a 50MHz 68882 should be around 50. I did not expect the FPU to run at 33MHz with this accelerator. The CPU score is around 12.7 which is in line with a 50MHz accelerator without an onboard cache. I bought it untested and there is no documentation or software online that I can find. Interware was based in Japan and now long gone. There is not much online to be found.

 

[Phipli]

Using PowerDemo from Daystar shows the 68030 @50MHz and the 68882 @33MHz. The SpeedOMeter 3.23 results confirm the FPU score is indeed running at 33MHz. The Performance Test result is 35 whereas a 50MHz 68882 should be around 50. I did not expect the FPU to run at 33MHz with this accelerator. The CPU score is around 12.7 which is in line with a 50MHz accelerator without an onboard cache. I bought it untested and there is no documentation or software online that I can find. Interware was based in Japan and now long gone. There is not much online to be found.

Hum. I wouldn't jump to that assumption. PowerDemo claims my 50MHz 040 is a 33MHz 040.

Do you have a continuity tester, or a multimeter in general?

 

[jasa1063]

Hum. I wouldn't jump to that assumption. PowerDemo claims my 50MHz 040 is a 33MHz 040.

Do you have a continuity tester, or a multimeter in general?

I have a mutlimeter.

 

[Phipli]

I have a mutlimeter.

Are the pins highlighted in blue connected together?

 

[jasa1063]

Are the pins highlighted in blue connected together?

View attachment 71758

I will check this weekend and let you know.

 

[zigzagjoe]

Just FYI, Speedometer's FPU scores are not great for measuring raw FPU performance. They are rather strongly influenced by CPU performance. So I would hold off from drawing any conclusions based on that.

Making some assumptions based on the SE30 design, I expect pin 6 of IC4 to be connected to those pins @Phipli pointed out.

 

[jasa1063]

Are the pins highlighted in blue connected together?

View attachment 71758

Yes, they are connected.