Interactive terminal system using a prepoll prior to transferring information from the controller to the work station

DETAILED DESCRIPTION An interactive terminal data processing system includes a high speed link controller (HSLC) and a number of work stations, all coupled in common to a single conductor coaxial bus.
Information is transferred between the HSLC and a selected work station at 750,000 bits per second.
A work station is normally operative in a background mode, that is, off-line from the HSLC.
The HSLC sends a block of information to a selected work station over the bus by sending a flag character followed by a work station address character, a control character, and a block of 1024 characters of information.
In order for a work station to be ready to receive this information, a prepoll message is sent by the HSLC over the bus which includes a flag character the work station address character, a cyclic redundant check character (CRC), and a closing flag character.
The work stations include a communications controller which is responsive to its work station address received from the bus to interrupt a microprocessor.
The microprocessor branches to a microprogram stored in a read only memory to condition the work station to receive the above block of information for storage in a random access memory.