Corrections to trivia

From: Eric Smith <eric_at_brouhaha.com>
Date: Tue Oct 6 13:37:45 1998

allisonp_at_world.std.com (Allison J Parent) wrote:
> Not quite. the F8 cpu (3850) was an incomplete system without the
> 385x (3851,6,7 PSU). It was very difficult to simulate the PSU in ttl
> as well.

Having used both the F8 and the LSI-11, I beg to differ. The F8 CPU was
a complete CPU on a chip. The PSU chip was most definitely not necessary.
The PC and data pointers were replicated on the PSU, but they did exist on
the CPU, and the CPU was responsible for making sure that the PSU always
had a correct copy of them. This is just an issue of efficient bus
utilization, and there have been other processors that have done this.

You might just as easily argue that any of the early Intel microprocessors
were not complete because you couldn't simply hang 1702 EPROMs or 2102
RAMs directly on the bus. However, I don't recall anyone in this discussion
previously claiming that a chip has to have a simple bus interface in order
to qualify as a microprocessor.

> The two ran in lock step just like the parts of the F14 CADC
> or the LSI-11 with it's MICROMS.

The main LSI-11 chip did not have the control store necessary to execute
the documented instruction set; that was in the MICROMs. The F8 CPU included
all the necessary instruction decode and sequencing on chip.

You could argue that the main LSI-11 chip was a single chip microprocessor
from the viewpoint of a microcode programmer. However, to the best of my
knowledge it was never used in systems without MICROMs to implement an
user-level instruction set (i.e., the LSI-11, Alpha Micro, and WD Pascal
Microengine).

> The 3870 was the single chip version
> of the F8.

That's true but it is an understatement. The 3870 was a single chip ONLY
version. It was not externally expandable.

> In some respect the F8 was like many early parts in that the
> CORE CPU was there but glue was needed to make it all work.
> (8080/8224/8228 for example).

Yes. Are you arguing that the 8080 is not a microprocessor?
Received on Tue Oct 06 1998 - 13:37:45 BST