# Low-Voltage Positive Emitter-Coupled Logic (LVPECL)

LVPECL is a 3.3 V differential signal standard that transmits one data bit over a pair of signal lines, thus requiring two pins per input or output. The voltage swing between the two signal lines is approximately 850 mV. While LVPECL input is supported for GPIO, external board termination is required for the LVPECL outputs. For more information about LVPECL33, see LVPECL Emulated (LVPECLE33) Output Mode.