Date: Sat, 10 Dec 2005 02:38:34 -0800 (PST) From: Gregg Eshelman <[EMAIL PROTECTED]>
There's also the Turbo 601 in 66 and 100 Mhz versions. The later 66Mhz ones were actually made with 100Mhz CPUs and some of the later 100Mhz ones got 110Mhz. A 66Mhz one with an underclocked 100Mhz CPU can be "overclocked" to 100,
The overclocking operation for the Turbo601/66 involves changing the bus multiplier for the PPC601 from 2X to 3X. Since the card runs on a 33.3333MHz clock, that ups the speed from 66MHz to 100MHz. Apparently the PPC601 doubles the incoming clock signal without any help. However, if you want it to triple the clock signal, it requires an external Clock Generator chip.
but it's a difficult operation that involves finding an out of production chip as well as the faster crystal, and moving some other surface mounted parts.
The external Clock Generator chip used by Daystar is the ICS9178. I believe that ICS's website is at <http://www.icstech.com>. That chip is discontinued, but there may be a useable substitute. That chip was pretty much designed for use with the PPC601, and since the PPC601 is out of production...
If you're willing to kill a PM8100/100 or 8100/110 or a Power Computing Power 100 or Power 120, you can scavenge the ICS9178 off of their motherboards. Unfortunately, it is not available on the 7200/120 board (I wouldn't have any quams about killing a 7200). That board uses a Motorola Clock Generator chip. Which implies the Motorola part could be used, but it has a different form factor and pinout from the ICS chip, so it'd be a pain to substitute.
One last note on overclocking the T601/66. When I wrote the article for Marc Schrier's page on converting the T601/66, the method I used was to compare a 66 and a 100 T601 and then move resistors (and add the ICS9178) until the 66 looked like the 100. I've since learned that the specified supply voltage for the PPC601 changed from 5V to 3.3V when they went from 66/83 to 100/120 speeds.
The output of the voltage regulators typically used is adjustable by changing the value of a couple of resistors. So it is entirely possible that the overclocking method described in that article changes the supply voltage of the PPC601 from 5V to 3.3V, which is a mistake since one does not change the actual PPC601 chip on the card. On the other hand, it worked when I did it, so perhaps I'm worrying about nothing.
I've not seen anything on overclocking the 100Mhz Turbo 601.
The problem is that the Turbo601 is very intolerant of having its bus clock speed changed. The stock bus speed is 33.3333MHz. The Turbo601 will work down to about 29 MHz--maybe 28--and up to maybe 35MHz if you're lucky. So if you tried to overclock the 100MHz version, the best you might do is go from 100 (3 X 33) to 105 (3 X 35).
I'm near certain that the ICS9178 and the PPC601 will support a 4X bus multiplier. With a bit of sleuthing, one might be able to modify the Turbo601/100 to run at 4X and downclock the bus to 30MHz for a 120 MHz (4 X 30MHz) upgrade. However, IBM's specs state that you need active cooling if you go over 100MHz, so one would need to add a Peltier Thermoelectric cooler to the PPC601. I'm not sure the IIci power supply has enough extra power to drive the cooler. Those things eat current.
The Turbo 601 has SCSI Manager 4.3 in its ROM, but it appears to be a buggy implementation.
Yeah, there's definitely something odd going on there. If one uses the JackHammer SCSI card with the Turbo601, one must disable SCSI Manager 4.3 in the Turbo601 CP. That doesn't get rid of SM4.3, it just gets rid of a version that gets in the way. Apparently it's present somewhere else as well (JackHammer Firmware?).
One of the Daystar guys once wrote that the Turbo601 basically has a set of 6100 ROMs on board. IIRC, all the Macs from the Quadra 660AV and 840AV forward have SM4.3 in their ROMs. So the PM ROMs on the Turbo601 have SM4.3 built-in as well, but as Gregg wrote, it doesn't work quite right.
That pretty well describes my whole experience with the Turbo601. It was an amazing piece of engineering, but there are so many odd incompatibilities and exceptions when using the thing, if you really want a PPC, then just get a 7100 or something.
After "overclocking" my Turbo601 from 66 to 96MHz (3 X 32MHz) and fiddling with it for a year, I finally sold the hacked T601 and my 16MB SIMMs and used the money to buy a refurbished Power 120 by Power Computing. Of course this was back when such things still brought hundreds of dollars.
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