On 2020-03-23 22:32, Clem Cole wrote:
On Mon, Mar 23, 2020 at 3:57 PM Johnny Billquist <b...@softjar.se
<mailto:b...@softjar.se>> wrote:
The VAX-11/750 used 2901 though...
750 was made out of custom CMOS gate arrays. The main adder was
analyzed as part of my thesis [long story - not for here, but a very
clever circuit. I would later get to know the guy that did it].
Now that you say it, it rings a bell. I must totally be mixing the 750
and 730 up...
Also, I know that there was an Intel 808x processor (85 I think) that
shipped in the 750, but it was not an FEP. It was limited to running
the cartridge tape controller. I don't remember how the console serial
port was done (the 780 it was part of the FEP). The 750 microcode did
the boot as someone else pointed out. I've forgotten how the microcode
was loaded on a cold start. I thought there was something in a
ROM/EPROM, but I've forgotten. I do know the cartridge tape unit was
needed to update the microcode and that was the only way to do it. But
I don't remember you need to have the tape on a cold reboot the like
floppies on a 780, but I could have forgotten.
Looking a bit at the documentation, both the console and the TU58 are
run directly by the VAX CPU. They are both just serial ports anyhow, so
not much to do for either, actually.
The microcode is in ROM, so not loaded at all. But there was a bit of
patch ram available to correct bugs in the microcode.
And NetBSD still have that microcode patch file in the distribution. It
originally came with Ultrix, I believe. And if NetBSD boots on an
11/750, it will patch the microcode. But I don't know what the patches
actually fix. Maybe someone else knows...
Not sure if you could update the full microcode on the machine. I
haven't seen anything suggesting it is possible in the documentation...
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: b...@softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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