semi-OT: text lites

From: Bert Thomas <bert_at_brothom.nl>
Date: Fri Apr 30 13:27:31 2004

John Allain wrote:
>
> There's a big Toshiba TMP80C49P that looks like a 'keyboard'
> MCU to me. Some minor things like Motorola SN74LS(05N,138N).
> Nearest the SIO port are just a few resistors and two
> transistors. At least one leg of the SIO goes directly to
> the toshiba. Looks non-RS232 then... Whatsit 5V instead of 15?

Not necessarily: you can convert the voltage levels with just a few
discrete components. Mostly in such cases the receiving voltages are
used to charge a capacitor that delivers the negative voltage for
sending data. In that case there must be a diode somewhere in the
neighbourhood as well.

Bert
Received on Fri Apr 30 2004 - 13:27:31 BST