HP9845 design article in EDN

Chuck Guzis cclist at sydex.com
Wed Nov 3 16:47:22 CDT 2010

On 3 Nov 2010 at 20:42, Tony Duell wrote:

> Interesting... Why specifically for me, though (other than I have an
> HP9845B which AFAIK uses the same I/O backplane PCB).

I seemed to recall that you specifically have an interest in the old 
HP 9800 series.  If you don't care for things such as this, I'll make 
a note to ignore them.

> I am also a little suprised by the comment that logic analysers didn't
> really exist at that time (not that a logic analyser would have been a
> lot of help fo this fault).  I am wondering how the older HP machines
> were actually debugged. Having repaired several of them, I find a
> logic alauyser to be next-to-essential. Even more so if the design is
> not known to be sound.

Oscope, in particular storage-tube scopes.

The HP 1600A dates from 1976 and was marginally useful.  The 1602A 
dates from 1978.  I remember getting one to evaluate from Electro-
Rents and thought it very cool, but didn't use it all that much.  We 
had a logic analyzer plugin for the Tek 7400 series scope frame that 
was good enough--and lots cheaper.


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