Data Handling Instructions

2. 14 Data Handling Instructions

3. Objectives • Use PLC instructions for moving data from one register to another. • Create stacks for storing and retrieving data from PLC memory. • Move data between tables. • Use PLC instructions for number system conversion.

4. Data Handling Instructions • Reading, storing, retrieving, and writing of data on ports and registers. • Moving or copying data to another register or file. • Converting data to a different number system. • Performing a logic operation on data.

5. Move (MOV). Masked move (MVM). FIFO load (FIFO). FIFO unload (FFU). LIFO load (LIFO). LIFO unload (LFU). Copy file (COP). Fill file (FLL). Convert to BCD (TOD). Convert from BCD (FRD). Convert from radians to degrees (DEG). Convert from degrees to radians (RAD). Data Handling Instructions (Cont.)

6. Index Register • Sometimes simply called a pointer. • A register that holds an address of a data. • Used to move a word into a specific address. • Data is placed in another data register.

7. Move (MOV) Instruction • Transfers a number into a register. • Transfers content of a register to another register.

8. Ladder Logic Diagram Using Index Register

9. Masked Move (MVM) Instruction • Hides or masks a portion of data prior to transferring it into a register.

10. Masked Move Example • Using masked move (MVM) instruction to read data from input module two (I:2) • Mask the lower byte of the data prior to transferring it into address B3:0.

11. Masked Move Example (Cont.) • Input module two (I:2) data ANDed with mask number FF00h to set lower bytes to zero. • Bits in the upper byte have same state as bits in I:2 module’s upper byte.

12. FIFO and LIFO • Like pallets, data registers can be stored and retrieved in two different ways: • First-in-first-out (FIFO). • Last-in-first-out (LIFO).

13. FIFO and LIFO (Cont.) • Concept of storing and retrieving pallets is similar to the way data is placed in and retrieved from a stack. • A stack in PLC or computer terms: • A group of consecutive data registers, or words, placed temporarily in a memory location, or buffer.

14. FIFO and LIFO (Cont.)

15. FIFO and LIFO (Cont.) • When stacking data: • Stack grows larger as data registers are placed in stack. • Stack grows smaller as data registers are retrieved from stack.

16. FIFO and LIFO (Cont.)

17. FIFO and LIFO (Cont.) • In FIFO operation, first item in stack is first item out of stack. • In LIFO operation, last item in stack is first item out of stack. • Push operation – placing an item in a stack. • Pop operation – retrieving an item from a stack.

18. FIFO and LIFO (Cont.) • Allen-Bradley SLC 500 PLCs have four instructions for LIFO and FIFO operations: • FIFO load (FFL). • FIFO unload (FFU). • LIFO load (LFL). • LIFO unload (LFU).

19. FIFO and LIFO (Cont.) • In PLC systems, stacks are created when stacks of integer words (i.e., double-byte data) are stored in the memory buffer. • Data can be transferred into a register or another memory location from the stack.

20. FFL Load Instruction

21. LFL Load Instruction

22. Copy File and Fill File Instructions • Data handling instructions used to store blocks of data in a PLC file: • Copy file (COP). • Fill file (FLL). • Can use these instructions to manually enter a file with constant numbers or data from another file.

23. Data Conversion • Data conversion instructions used to convert content of a PLC register from: • One number system to another number system. • One unit system to another unit system.

24. Data Conversion Instructions • TOD instruction: • Converts binary number in source register to binary coded decimal (BCD). • Places result in destination register. • FRD instruction: • Converts BCD number in source register to binary. • Places result in the destination register.

25. Data Conversion Instructions (Cont.) • DEG instruction: • Converts angle value from radians to degrees. • RAD instruction converts value of an angle from degrees to radians.

26. Convert to BCD (TOD) and Convert from BCD (FRD)