When COM ports are configured as Modbus slaves, the internal PLC tags are mapped to the modbus addresses as given in the following table:
PLC Tag description | Reg. Addressing | Bit Addressing | Modbus address |
I/O register | XW(400) | X (6400) | 440001 - 440400 |
| YW(400) | Y (6400) | 441001 - 441400 |
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Auxiliary registers | B0000 to B4095 | 442001 - 442256 | |
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System Registers | Not Mapped | 420001 - 420256 | |
Timer Registers | Not Mapped | 400001 - 400256 | |
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Counter Register | Not Mapped | 410001 - 410256 | |
Data Registers | Not Mapped | 450001 - 454096 | |
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Retentive Registers | Not Mapped | 430001 - 431400 |
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Index Register (I,J,K) | I | Not Mapped | 443001 |
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| J | Not Mapped | 443002 |
| K | Not Mapped | 443003 |
Configuration MW registers | MW(1600) | M(25600) | |
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COILS: |
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| TR0- TR15 |
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Input Coil (R) |
| X (6400) | 000001 - 006400 |
Output Coil (R/W) |
| Y (6400) | 010001 - 016400 |
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System Coil (R/W) |
| S 0000 to S 0099 | 020001 - 020100 |
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Internal Coil (R/W) |
| B 0000 to B 1023 | 030001 - 034096 |
Timer Devices (256 bits = 16 words) |
| T. 000 to T. 255 | 021001 - 021256 |
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Counter Devices (256 bits = 16 words) |
| C. 000 to C. 255 | 022001 - 022256 |
Configuration MW coils |
| M(25600) | 035001 - 060600 |
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