How to lose most of an an entire collection in one shot

Tony Duell ard at p850ug1.demon.co.uk
Sun Jun 21 15:29:54 CDT 2009


> 
> I really like the 125 for several reasons.  First, it has an HPIB 

I wonder why you like the HP125 and not the HP120, given that they're 
almost the same machine electronically. All the points you make apply to 
the 120 as well.

> interface for disks, etc.   That interface also allowed it to be a 
> controller for calibration instruments.  It also used an easy to create 

Sure, but most HP machines have HPIB :-). The HP120 doesn't properly 
support the HPIB port in the BIOS (IIRC there's no BIOS function to read 
from an HPIB device) so you pretty much have to talk to the 9914 
directly. Not a big problem, but if you get it into the wrong state you 
may find you can no longer talk to the disk drives. 

For talking to instruments, I prefer to use an HP9000/200 machine with a 
second HPIB port (HP98624). Firstly there's much better standard software 
support for the HPIB interface, and secondly, if one of the instruments 
'hangs the bus' (likely in my case as I might well be repairing said 
instrument), I can still talk to the disks.

> disk format.  Also handy.
> 
> 
> > When I said I didn't like the design of the HP120, I didn't mean the 
> > 'looks ' of the machine. I meant the electronic design -- a separate 
> > terminal processor communicating with the application processor through a 
> > little 'mailbox' and a very strange video circuit.
> >   
> 
> I worked for two companies which made terminal / PC combo devices.  I 
> suppose I have a weakness for them.  The 125 behaved as a decent 
> terminal on an HP 3000, and ran as a CP/M computer simultaneously, 
> allowing a switch between disparate processes that the standard PC world 
> wouldn't see for many years.  The "strange" circuitry made it easy for 
> the user to alternate processes, and allowed communication between

It's not so much that, but rather the actual design of the video circuit. 
It uses that National 8350 chip (actually a differently mask-programmed 
one for a different screen format). That's a strange chip, it interrupts 
the Z80 at the start of each character line, and fills an 80 byte shift 
register with characters. 

And then there's the attributesm which are set on a character line basis. 
Basically, every character is either normal or enhanced (decided by bit 7 
of the chracter code). You can only have one type of enhancement in a 
given line. So you could have normal and underlined characters in the 
same line, but you can't have normal, inverse, and underlined characters 
all in the same line.

Another problem is that AFAIK there's no official way for a CP/M program 
to set the parameters of the serial ports (not even the 'printer' port). 
The serial chips are on the terminal processor bus, there's no direct way 
for the application processor to talk to them. There's an undocumented 
way to run code on the terminal processor (in that at least one HP 
application does that), but I can't find out how to do it.
 
> them.  It's appropriate to have complex hardware and software to make 
> the use of the machine easier.  At least, that's my theory.  The HP 125

Sure, but I don't think the HP120 falls into that category. 
 
> was both pretty and easy to use, as an HPIB controller, an HP terminal, 
> and as a CP/M machine.

I'd much rather have an HP9000/200....

-tony



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