Gaps in the collection (was Re: rarest computers. )

From: Vassilis Prevelakis <>
Date: Mon Aug 9 04:41:19 2004 (Tony Duell) wrote:
> Talking of HP using 555 timers, they used one to drive the power-on light
> in the HP86 (and I assuem the HP97). [...]
(nitpicking here, you are talking about the 87)

> So the LED is dark if the machine is off, on steadily if the machine is
> on and no error (555 is held reset, so the output is low all the time),
> and blinks (controlled by the 555) if there's an error.

Actually the LED blinks when the machine is busy (e.g. running a program).
This is very neat as with the HP85 you sometimes do not know whether the
program has finished or is still running.

Received on Mon Aug 09 2004 - 04:41:19 BST

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