The asynchronous serial data needs also a word synchronization. We wait for a falling edge in the demodulator output that signals the beginning of a START bit. Then we wait for a half bit time and we check that the current bit value is still ``0''. If this check fails we just wait for another START bit.
When a valid START bit is detected we call the DPLL routine one time for each following bit. The data bits, parity bit and STOP bits are recovered in this fashion. The recovered parity and STOP bits are checked against errors and the character is marked as erroneous if this check fails. The character recovery routine waits until all the STOP bits are read as ``1'' allowing for a more probably good START bit in the following character.