A multistation single-channel communication bus system accommodates master stations and slave stations. A master station arbitrates, detects arbitration outcome, and formats. A frame has slave address and slave control signals and accommodates a plurality of data byte periods up to a first maximum, each period accommodating an acknowledge bit. Upon absence of the acknowledge bit the associated data byte is repeated. For intended transfer of a message whose data byte length would exceed said first maximum the message is divided into partial messages each of an associated frame data byte count below said first maximum, and assigned to a respective bus frame. For each frame, both byte periods and received acknowledge bits are counted. If the first maximum is attained earlier by said data byte period number than the frame data byte count by the acknowledge bit number, the frame has failed. Any transfer in that frame is then ignored and a repeat is undertaken.