Possible Upgrade Idea?

[CC_333]

Hi,

I don't know a whole lot about these things (yet!), but I was curious if anybody has somehow replaced the stock SCSI chip with something faster in, say, the SE/30.

People add on SCSI chips to things like the Mac 512K (by way of upgrade cards and such), so it's at least plausible, in my opinion. Non-trivial, perhaps, but plausible.

I don't have much knowledge to back this up yet, but I thought I'd throw the idea out to the wind to see what happens.

c

 

[Bunsen]

Hm. One could possibly do something like a PDS version of the Nubus SCSI cards, and adapt their drivers. Or did you mean literally replacing the SCSI IC on the motherboard?

 

[CC_333]

Hi,

I meant to replace the actual SCSI chip with something pin compatible with the one that's there, but faster/more capable.

A PDS solution would probably work as well, if the chip replacement proves too impractical.

c

 

[ClassicHasClass]

It's not just pin compatibility; it needs to have the same registers as well. There are some upwardly compatible SCSI chipset series IIRC, but that doesn't mean that the SE/30 used one of them.

 

[trag]

The Macs that had SCSI chips added were the early pre-Plus Macs. In most of those cases the old host Mac had the new Plus ROMs (or 512KE ROMs) such that support for the SCSI chip was already in the firmware (ROM) even though the chip was absent.

In some very early cases an extra ROM (EEPROM) chip was added which contained the firmware needed for the SCSI chip.

In order to change the existing SCSI chip on a Mac, it doesn't just need to be pin compatible, it also needs to operate in exactly the same way, such that the firmware that operates it will still work. The registers also need to be at the same addresses, as CHC pointed out, and these two things can be related.

The SE/30 uses the 53C80 SCSI chip. The next step up is the 53C94 or 53C96 and it's not really substantially faster. After that, one gets into SCSI enhancements such as Fast, Ultra, and/or Wide. At that point, newer firmware would definitely be needed.

A faster chip could be added as a PDS card, but at this time, if one were going to build a PDS card, and was going to have to write firmware anyway, one might as well design a SATA card or maybe a USB card.

 

[CC_333]

The SE/30 uses the 53C80 SCSI chip. The next step up is the 53C94 or 53C96 and it's not really substantially faster. After that, one gets into SCSI enhancements such as Fast, Ultra, and/or Wide. At that point, newer firmware would definitely be needed.

Maybe that would be getting rather hard, but perhaps one could write some sort of patch which would contain the necessary firmware for the new chip.
Exactly how much faster is the 53c94/96? We can probably only go so fast, due to all the bottlenecks elsewhere in the system (the 16 MHz CPU probably being the most obvious). These may be fast enough to warrant the upgrade.

A faster chip could be added as a PDS card, but at this time, if one were going to build a PDS card, and was going to have to write firmware anyway, one might as well design a SATA card or maybe a USB card.

Yeah, I suppose. But sticking with SCSI would avoid any incompatibilities the software (OS, ROM, etc.) might have with newer technologies (such as SATA and USB), at least for boot disks.
Maybe it could be some sort of all in one card, with relatively fast SCSI, SATA and USB. That is probably a bit too ambitious of me, but I like the idea nonetheless.

There must be someone in the world who could design and implement such a device.

c