On 3/18/2013 12:38 PM, William Donnelly wrote:
> How hard would it be to make "hot-swap" 'cartridges' like old-style
> video games, so you can just plug in a "ROM" program. Or even ROM/RAM,
> Or cold swap. Whichever is easiest / cheapest and doable.
Hot swap is harder, because you have to worry about making the power and
ground connections first, and then holding the logic levels to a safe
level until they are all properly connected.
The classic video game cartridges used connectors with the power and
ground pins longer than the others, so they connected first. They
contained read-only memory, so there was no danger of accidentally
changing the data.
If the cartridge has RAM in it, then it has to include a way to write
protect the RAM when it is removed and while plugging it in or out.
The device the cartridge is being plugged into also needs to make some
allowances. Plugging it in can't glitch the power supply. For example,
the cartridge can't have a big filter capacitor that momentarily shorts
the power supply before it charges. It needs some series impedance to
limit the peak current.
Similarly, the data lines need buffers so the cartridge can't "glitch"
them high or low during plugging or unplugging and so crash the computer.
Ring the bells that still can ring
Forget your perfect offering
There is a crack in everything
That's how the light gets in.
-- Leonard Cohen, from "Anthem"
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm