On Jul 27, 4:28 pm, PeterH <[email protected]> wrote:
> On Jul 27, 2009, at 1:37 PM, Doug McNutt wrote:
>
> > But do the ANS's connect with OS 10.4 and above which will not talk
> > AppleTalk over Ethernet?
>
> An ANS has a proprietary processor which, although a 604e, just as in
> the 9500, has lots of added circuitry for testing and checking.
>
> It is more an IBM RS/6000 than it is an Apple PowerMac 9500.
Depending on the context in which a person is thinking, that may be a
little misleading.
The ANS has a CPU card, in a similar manner to the X500/X600 family.
The CPU on the ANS CPU card is a plain old PPC604e. It's not a
special CPU chip.
The card, on which the CPU resides, has a different form factor and
pinout from an X500 CPU card. Additional test signals, which are
present on all PPC604e chips, are brought out on the ANS CPU card. It
also handles the system clock in a very different fashion. But there
isn't a bunch of different circuitry present. It should, in theory,
be possible to adapt a Mac CPU card to the ANS. I made one stab at
it and then set it aside.
For those who might be interested (warning: fiddly little board
electronics details follow)...
The X500/X600 family of Macs have the system clock on their CPU
card. This system clock goes to a chip called a Clock Buffer. The
clock buffer splits the original oscillator signal into several
seperate clock signals. One of these clocks goes to the CPU chip on
the CPU card. The other clock signals go off the CPU card and
through the CPU connector. From there they run to the logic board
components which need the system clock, such as Hammerhead (CPU bus
arbiter/memory controller) and Bandit (CPU-PCI bridge).
The ANS also has the system clock on the CPU card. However, the
clock buffer is not on the CPU card. Instead, the clock signal runs
through an inverter (presumably to increase signal power and clean up
the waveform) and then off the card to the logic board. On the
logic board it then runs through another inverter and then to a clock
buffer chip, which splits it into several clock signals. Two of
these then run back to the CPU card connector, and once back on the
CPU card, one of the clock signals is fed to the CPU. The other CPU
card clock signal is available for dual processor cards, but not used
in practice. The clock signals which stay on the logic board go to
the same components that they go to on a 9500.
So the ANS puts the clock buffer on the logic board, which then feeds
a clock back to the CPU card, while the X500/X600 puts the clock
buffer on the CPU card.
So, if one tries to adapt an X500 CPU card to the ANS, one finds that
the clock signals are a pain. You can route one of the X500 CPU card
clock signals, which would normally go to the X500 logic board, into
the single ANS clock signal input. But your X500 CPU is being
driven by a clock signal which arrives long before the ANS clock
signal would, because the ANS clock signal has to run off the CPU
card, go through the clock buffer and then travel all the way back.
This results in all the signals from the X500 CPU being out of whack
with all the components on the ANS motherboard, because their clocks
are too far out of phase (the CPU clock is too early) with each other.
The solution should be a clock chip with a phase shifter and
feedback. These are commonly available parts. One feeds it the
original clock signal as an input (X500 CPU card clock), and then it
outputs a clock signal at the same frequency. Then you also feed it
the resulting clock as another input (in this case, the clock signal
from the ANS logic board which would ordinarily drive the ANS CPU) and
the chip adjusts the phase of its output until the two inputs are in
phase with each other. Voila, the ANS motherboard clock and the X500
CPU clock are now in phase with each other.
Of course, I haven't gotten it to successfully work, but I haven't
worked on it in six or seven years either.
Jeff Walther
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