This enables or disables single-bit error correction in the ATM Header Error Control (HEC) algorithm on this port. Enabling HEC correction lets this specific port automatically fix single-bit errors in cell headers rather than discarding the cell outright, directly reducing the counts reported by pportHcsSevereErrors at the cost of slightly more processing per cell; disabling it means even single-bit header errors get treated as uncorrectable. A port with pportHECMode disabled would show every header bit error, even trivial single-bit ones, counted as a severe uncorrectable HCS error, whereas enabling it would shift many of those into the merely-correctable pportHcsErrors count instead.