Definition of block

in message transfer, a physical division of a message (a complete unit of communication). NOTE-In SECS-I, each block has a block header (a 10-byte data element used by the message and transaction protocols) and up to 244 bytes of data. For compatibility with SECS-I, SECS-II also recognizes the same block length for data; however, in SECS-II there is only a message header, not a header for each block. [SEMI E4-91 and E5-92]