Re: Q: ADT-transfers on Franklin ACE 2200 + Super Serial Card II

[Alex Freed <alexf@mirrow.com>]

John B. Matthews wrote:
> Alas, it mentions using an Ohm meter to detect open- and short-circuits 
> in many contexts, but there's nothing on measuring TTL levels under 

A very inexpensive logic probe is great for that, especially if
you don't have a scope.

> program control to diagnose an SSC. I'm sure a VOM responds too slowly 
> to see changes on TXD, but maybe you could measure a constant level. 
> Clearing bits 2-3 of $C08A+slot should make RTS high. I'm guessing.

I don't think this is in any FAQ - I just came up with a simple method
to find if RS232 signals are present with only a DVM. You also need
a diode and a capacitor. A given RS232 signal should be at -12V or so
at rest. If it is pulsed, the pulse would go to +12V or so. Connect
it to a capacitor via a diode.

Signal----------->|--------0-------||-------GND

"0" is the place to connect the DVM. It should read zero till pulses
start coming. Then it may read up to +12V, as DVMs are high impedance.


Another method is using an LED with a resistor. At 300 baud it will 
blink visibly.

-Alex.