From: "Terry Mathews" <[EMAIL PROTECTED]> Subject: Re: How to rate one's bus speed? Date: Thu, 24 Jul 2003 22:58:27 -0400
But I will bow to the experts. My machines must run under different
For whatever reason, all the processor cards you tried must have utilized the same or similar clock speeds. Believe it or not, the processor card tells the motherboard what clock speed to run at. That's why most G3 and G4 ZIF carrier cards have some sort of settings for the user to configure.
To elaborate a bit on what Terry wrote---he's absolutely correct. The memory bus speed on the x500 and x600 (and related clones) machines is set by the CPU card.
There is no oscillator on the motherboard which provides a memory/CPU bus clock. There's an oscillator (33.3333) for the PCI bus, and one for the sound circuitry and one for some of the other I/O, but none for the memory bus.
Pins 9 through 14 in the CPU slot connector provide the memory/CPU bus clock signals. Those signal originate on the CPU card, go through pins 9 through 14 on the CPU connector and tell the components on the motherboard what the bus speed is for the CPU card that is installed.
There are six of them because the signals are not split. It's one clock signal per component. So one of them goes to the memory controller chip (343S1190), one goes to the PCI controller chip (343S0020) and I'm not sure where the other four go. In the 9500 and 9600 one would go to the other PCI controller chip. In the 7300 - 8600 one would go to the video controller chip called CHAOS/Control. Two may go to the Data Path controller (343S1141) but I'm not certain about that and I've never traced it out. I'm pretty sure there is at least one and maybe two extras that don't actually go anywhere.
Apple originally intended this architecture to be capable of supporting up to four "bridges" on the CPU bus. That would mean four Bandit chips running twelve PCI slots, or three bandit chips and one built in video, etc. But they never went beyond two in any machine.
Jeff Walther
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