The block transfer instruction is normally used to transfer up to sixty-four 16-bit words of data in one processor scan from I/O modules to or from the data table. It is used with intelligent I/O modules, such as PID, analog, ASCII, thermocouple, or encoder/counter modules. In most PCs, the block transfer instruction moves only one word data per scan. The block transfer instruction can be performed as a read, write, or bidirectional operation, depending on the I/O module being used.
The programming format for both a block transfer read and write instruction are the same and have the following meanings:
1. Data address is the address in the accumulated area of the data table.
2. Module address is determined by the rack (R), module group (G), and slot (S)
numbers.
3. Block length is the number of words to be transferred.
4. File is the address of the first word of the file.
5. Enable bit (EN) is automatically entered based on the module address by the processor.
It is set ON when the rung containing the instruction is true.
6. Done bit (DN) is automatically entered based on the module address. It remains ON
for one processor scan following a successful transfer.