Fixing small plastic... things

Tony Duell ard at
Thu Dec 9 16:00:12 CST 2010

> On Wed, 8 Dec 2010, Tony Duell wrote:
> >> No, I haven't. The objective is to make a precise gate-level simulation
> >> of the calculator, both for understanding and which can be used to
> >> track down faults in a broken instance of the real thing. Patents
> >> generally don't provide the level of accuracy for that objective, so it
> >> generally doesn't occur to me to look to patents for these purposes.
> >
> > As n aside, some of the HP desktop calcualtor patents are very detailed,
> > and include sechematics, commented firmware source, extension ROM
> > sources, and so on. But as you imply, there are often suble differences
> > between the machien described i nthe patent and the actual prodcution
> > model. I regard these patents as a very useful resource and well worth
> > reading, but you need to check against an actual machine.
> Sure, but the patents help identify signal names and understand the 
> priciples of the machine. You can't easilly find out how a machine works
> by just looking at the flip-flop or some random logic. We had to repair 

Well, maybe some people can't, but there are plenty who can :-). More 
seriously, this is really what reverse-engineering is about, not just 
tracing out the schematic, but understanding what it is saying. 

> some Friden 132 boards just a few weeks ago, the block diagrams and 
> descriptions in the patents were quite helpful.

I think we're saying the same things. Certainly for the HP machines 
(which I am more familiar with), the patents are very useful. They will 
help you understnad what is going on in the real machine. However, if you 
attmept to repari a prodcution machine using the patent as a 'service 
manual' with no more thought then you will run into problems. The machien 
in the patent and the actuall machine are not quite the same. If you use 
the patent intellegently, examine the actuall hardware and see how it 
relates to the descriptions and diagrams in the patent then you'll sort 
it out.


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