Data Communication Processor
A data communication (command) processor is an I/O processor that distributes and collects data from remote terminals connected through telephone and other communication lines. In processor communication, processor communicates with the I/O device through a common bus i.e. data and control with sharing by each peripherals. In data communication, processor communicates with each terminal through a single pair of wires.
The way that remote terminals are connected to a data communication processor is via telephone lines or other public or private communication facilities. The data communication may be either through synchronous transmission or through asynchronous transmission. One of the functions of data communication processor is check for transmission errors. An error can be detected by checking the parity in each character received. The other ways are checksum, longitudinal redundancy check (LRC) and cyclic redundancy check (CRC).
Data can be transmitted between two points through three different modes. First is simplex where data can be transmitted in only one direction such as TV broadcasting. Second is half duplex where data can be transmitted in both directions at a time such as walkie-talkie. The third is full duplex where data can be transmitted in both directions simultaneously such as telephone.
The communication lines, modems and other equipment used in the transmission of information between two or more stations is called data link. The orderly transfer of information in a data link is accomplished by means of a protocol.