The data required by the user program is stored in data block (DBs and DXs). No STEP 5 operations are programmed in these blocks. Data can be following types:
• Arbitrary bit patterns, e.g., for plant status indications.
• Numbers (Hexadecimal, binary, decimal)
• Alphanumeric characters.
Generation of a data block on the programmer begins by specifying a data block number between 1 and 255. DW 0 to DW 255 can be addressed via load and transfer operations. Data words > 255 can be addressed using O B180.
One word is reserved in program memory for each data word. The programmer also generates a block header for each data block, the header takes up five words in program memory. Data blocks DB 2, 3 and 4 are interface blocks between the NC and the PLC 135 WB. The programmer prevents deletion and modification of these blocks. Below is a structure of data block.
Data block can be called unconditionally only. Once called, a data block remains in force until the next is invoked. User data blocks must not conflict with those required by the system.
A data block can be programmed in an organization, program, function or sequence block. The “C DB xxx” or “CX DX 200” command calls a data block. Below is example of transferring the content of data word 1 of data block 10 to data word 1 of data block 20.
