Appendix B: Profibus™ DP Slave Communication
How Addressing Works
PLC addressing is in byte and uses the scheme shown in FIG. 66.
Byte 0
Word 0
Byte 1
Dword 0
Byte 2
Word 2
Byte 3
Byte 4
Word 4
Byte 5
Dword 4
Byte 6
Word 6
Byte 7
Byte 8
Word 8
Byte 9
Note how a Dword or word address starts at the address of the first byte included in it.
FIG. 66. PLC Addressing Scheme
The Gateway addressing follows a different scheme, as shown in FIG. 67.
This means that the address number will be different when accessing words or Dwords in the Gateway data tags than the PLC. Table 6 shows the address relation- ship for integer tags mapped as word in the Gateway.
Byte 0
Word 0
Byte 1
Dword 0
Byte 2
Word 1
Byte 3
Byte 4
Word 2
Byte 5
Dword 1
Byte 6
Word 3
Byte 7
Byte 8
Word 4
Byte 9
Here, the word or Dword addresses follow the nor- mal numeric increment and are not directly related to the word or bytes they are composed of.
FIG. 67. Gateway Addressing Scheme
Table 6: Addressing Relationship
|
| PLC |
|
| Gateway |
| ||
|
|
|
|
| ||||
Block Type | Input (bytes) | Output (bytes) | Input (words) | Output (words) | ||||
|
|
|
|
|
|
|
|
|
64 words in, 64 words out | 256 | ...383 | 256 | ...383 | 0... | 63 | 0... | 63 |
|
|
|
|
|
|
|
|
|
16 words in | 384... | 415 |
| - | 64... | 79 |
| - |
|
|
|
|
|
|
|
|
|
5 words out |
| - | 384... | 393 |
| - | 64... | 68 |
|
|
|
|
|
|
|
|
|
70 | 312785C |
