16 May
2005
16 May
'05
4:29 p.m.
Tony, the HP250 CPU is said to be the same as the
9845* except for
different microcode. Reference this website if you can:
http://www.hp-eloquence.com/history/history.html
YEs, but _which_ 9845 processor?
An HP9845 has 2 processors (not counting the graphics accelerator that
may be in the monitor). One handles I/O (the 'Peripheral Processor
Unit'), the other runs user programs (the 'Language Processor Unit'). In
most machines, these are those HP custom hybrid modules with a large
die-cast heatsink on top, a bit like the processor in the 9825, but with
different pinouts, etc.
Soem machnies (and mine is one of them) have the high speed language
processor option. This replaces the LPU board with its processor with a
set of 3 boards linked by a little backplane on top. One of the boards
plugs into the main backplane slot that takes the normal LPU board. The
other 2 hang over the side of the cardcage. These boards contain (amongst
otehr things):
Interface PCB : Bus buffers, abritration logic, some processor registers
Data path : ALU (4 off 2901), condition logic, microcode branch PLA, ALU
decode PLA
Control : Micorocode PROMs, sequnecer (2910), BCD adder and shifter, more
registers
I am pretty certain than the 2 processors are object-code compatible. But
I am alos sure that schematics are totally different. I will take a look
at the ose HP250 diagrams if I get a chance (no, I am not going to spend
5 hours downloading them here!) to see what that did. But i suspect the
hardware will again be different.
I feel this may give you something to work with as you reverse engineer the
9845. You didn't say, and I assume it to be very much the case given the
lack of tech manuals for our own 9825 machines, that there was any tech
FWIW, a reverse-engineered 9825/9831 schematic is on the HPCC schematics
CD-ROM (along with similar diagrams for the 9100B, 9810, 9830, 9815, some
late rmachines, and most of the handhelds)
-tony