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  1. 1. Memory types  Process-image input register (I) Format: Bit Byte, Word, Double Word  I[byte address].[bit address] I0.1 I[size][starting byte address] IB4 Process-image output register (Q) Format: Bit Byte, Word, Double Word  Q[byte address].[bit address] Q1.1 Q[size][starting byte address] QB5 Variable memory area (V) You can use V memory to: store intermediate results of the control logic operations. • store other data pertaining to your process or task. • Format: Bit Byte, Word, Double Word 81 V[byte address].[bit address] V10.2 V[size][starting byte address] VW100
  2. 2. Memory types  Sequence control relay area (S) They are used to organize machine operations or steps into equivalent program segments. SCRs allow logical segmentation of the control Format: Bit S[byte address].[bit address] S3.1 Byte, Word, Double Word S[size][starting byte address] SB4  Special memory bits (SM) The SM bits provide a means for communicating information between the CPU and your program. You can use these bits to select and control some of the special functions of the S7-200 CPU, such as: • A bit that turns on for the first scan cycle • Bits that toggle at fixed rates • Bits that show the status of math or operational instructions Format: Bit SM[byte address].[bit address] SM0.1 Byte, Word, Double Word SM[size][starting byte address] SMB86 82
  3. 3. Memory types  Local memory area (L) The S7-200 PLCs provide 64 bytes of local (L) memory of which 60 can be used as scratchpad memory or for passing formal parameters to subroutines. Format: Bit L [byte address].[bit address] L0.0 Byte, Word, Double Word L [size] [starting byte address] LB33 83
  4. 4. Memory types  Analog inputs (AI) The S7-200 converts a real-world, analog value (such as temperature or voltage) into a word-length (16-bit) digital value. You access these values by the area identifier (AI), size of the data (W), and the starting byte address. Since analog inputs are words and always start on even-number bytes (such as 0, 2, or 4), you access them with evennumber byte addresses (such as AIW0, AIW2, or AIW4),as shown in Figure Analog input values are read-only values. Format: AIW [starting byte address] AIW4 84
  5. 5. Memory types •Analog outputs (AQ) The S7-200 converts a word-length (16-bit) digital value into a current or voltage, proportional to the digital value (such as for a current or voltage). You write these values by the area identifier (AQ), size of the data (W), and the starting by address. Since analog outputs are words and always start on even-number bytes (such as 0, 2, or 4), you write them with even-number byte addresses (AQW0, AQW2, AQW4), Format: AQW [starting byte address] AQW4 85
  6. 6. Replacing Relay by PLC First step- We have to translate all of the items we're using into symbols the plc understands A contact symbol A coil symbol 86
  7. 7. Second step - We must tell the plc where everything is located. In other words we have to give all the devices an address. Final step - We have to convert the schematic into a logical sequence of events. 87
  8. 8. Ladder Diagram and Programming: Load: The load (LD) instruction is a normally open contact A Load (contact) symbol LoadBar: The LoadBar instruction is a normally closed contact. A LoadBar (normally closed contact) symbol 88
  9. 9. Out :The Out instruction is sometimes also called an Output Energize instruction. The output instruction is like a relay coil An OUT (coil) symbol OutBar: The outbar instruction is like a normally closed relay coil An OUTBar (normally closed coil) symbol 89
  10. 10. Logic elements 90