Topic summary
RS-232-C
Extracted from the Wikipedia article RS-232.
Connectors
Presence of a 25-pin D-sub connector does not necessarily indicate an RS-232-C compliant interface. For example, on the original IBM PC, a male D-sub was an RS-232-C DTE port (with a non-standard current loop interface on reserved pins), but the female D-sub connector on the same PC model was used for the parallel "Centronics" printer port. Some personal computers put non-standard voltages or signals on some pins of their serial ports.