Abstract: A bus extender and data transmission method in which a continuous train of message frames of fixed size is sent along a dual serial link in both directions simultaneously. There is no handshaking between extenders unless a transmission error is detected. Message frames are constructed at a rate which is independent of serial link length and the bus data transfer rate. Each extender is divided into a bus handshake layer which sends and receives data and signals from a local bus, a management layer which continuously constructs message frames, responds to commands and receives and decodes incoming messages from a remote extender, and a transport layer. The transport layer has shift registers and encoders to receive messages from the management layer and transmit them over the serial link and has a memory to store up to 30 messages in the event of a retransmission request. The transport layer also receives messages from the serial link, checks for valid error-free messages and sends them to the management layer.

Abstract: A bus extender which accepts data from a parallel data bus and extends the bus by means of a serial link to another parallel bus. The bus extender comprises a local and remote station or terminal, each having a transmit and receive section. A transmit terminal receives a data frame from the parallel bus and decomposes the frame into data and management sub-frames. The local and remote terminals exchange management sub-frames, thereby starting the transmission process. A data sub-frame is then transmitted from the local to the remote station and a management sub-frame is returned from the remote station indicating receipt of the data sub-frame. Other sub-frames may be exchanged for specialized purposes, such as polling and error signalling. Specialized messages may be identified by tagging sub-frames with message codes. At the remote station, the original management and data bits are reassembled into a single data frame with placement of the bits in the same order as originally appeared at the local station.