Stanley L. Fickes - San Jose CA Bernard E. Stewart - Campbell CA Robert J. Grady - Windsor CA Rick L. Reagan - Santa Clara CA John Piccone - San Jose CA Richard C. Allen - Los Gatos CA
Assignee:
Photonics Corporation - Campbell CA
International Classification:
G08C 2502 H04L 114
US Classification:
371 34
Abstract:
An infrared RS 232 communication link protocol is particularly suited for correcting any errors introduced during a transmission of information. The information is transmitted from a transmitting station to a receiving station. Each of the stations has a control counter each of which toggles between a logic 0 and 1. The control counter for the transmitter and the receiver are phase locked so that all errors may be corrected. The receiver echoes each data bit back to the transmitter which compares the echoed data to the transmitted data. If there is a match, the transmission was successful. If there is no match, the data must be retransmitted. A retransmit control character RTXx is sent to indicate that the receiver should discard the previous character and prepare for a retransmission of the character having the error. Under the proper circumstances and if the counters are still phase locked, the receiver then discards the previously stored character and inverts the counter. If the receiver detects that it has received an erroneous character, such as one having multiple or no PPM pulses, the receiver will simply respond with the reject control character REJ.
An improved tape timer is achieved by using pulses generated by a control track previously recorded on magnetic tape to determine the magnitude of phase shift between said control track pulses and pulses generated by a mechanical tachometer in contact with the magnetic tape. The pulses generated by said mechanical tachometer are counted and said counting sequence used to generate a pulse to up-date a tape timer. In response to a detected phase shift, the count sequence is dynamically adjusted by an amount determined by the magnitude of the phase shift in such a manner as to reduce said phase shift.
