On 06/27/2016 05:34 AM, Paul Koning wrote: > How high was "too high"? The RS232 standard rules for allowed output > voltages are surprisingly lenient (3 to 15 volts, positive or negative > for space and mark respectively). Mark (not space) was around +3V, ha :-) I have no idea how the VT52 was making sense of that, but it was, quite reliably. --FritzM.