HP98035 Real Time clock and AC5954N clock chip

[Eric Smith]

On Thu, Jun 6, 2019 at 9:57 PM Tony Duell via cctalk <cctalk at classiccmp.org>
wrote:

> HP were fond of using NiCds as shunt regulators at that time. The did
> it in many of
> their handheld calculators (HP20 series 'Woodstock', HP30 series
> 'Spice', etc). In
> those it wasn't normally a problem (the calculator electronics drew
> enough current to
> pull the voltage down) except in machines with 'continuous memory'
> (battery backed
> RAM). There, if the machine it turned _off_ the RAM is the only thing
> drawing current
> and it doesn't draw enough to pull the voltage down below the zapping
> level.
>

The should have paralleled the battery with zener with a voltage somewhat
above the normal battery charging voltage but below the abs max rating of
the power supply pins of the chips. They saved maybe ten cents by omitting
that.