FCDEV3B V2 new thoughts

[Pičugins Arsenijs]

> What we really need is a circuit that will cause the
> reset line to be pulled low during system boot (Calypso reset to be
> more precise), and then leave it high afterward, no matter what the
> Calypso subsequently does after it has booted.

The simplest (and workable) solution contains three components:

https://cdn.hackaday.io/images//835881528719783422.png

On bootup, capacitor is discharged, so the RST is pulled low - but then,
it's slowly getting charged through the resistor, so it's slowly being
pulled high, and it remains high for until power is removed. The diode is
there so that, if the power is removed for a short time, the capacitor is
discharged into the power rail - so that the device will be reset after a
power glitch / short-term power removal. If your chip(s) don't have
hysteresis RST inputs, you might want to put a single-gate non-inverting
buffer - or some other gate if you want to use RST signal from other
sources at the same time.

This solution is what's used on SSD1306 and SH1106 OLED displays
that I use, which require RST pin to be brought low for a period of time
after power is applied. It's also used for cheap power-on-reset otherwise.

Cheers!
Arsenijs.