The following example shows how the PROFIBUS protocol actually works with the PM130 PLUS. The HMS PROFIBUS master simulator is used to demonstrate the contents of the master PLC output/input buffers. For communication details, refer to the PM130 PLUS PROFIBUS Reference Guide.


First note that the meter uses a big-endian order of bytes, as it's common in PROFIBUS. This means that all word and double word sized data is transmitted a high order byte first followed by a low order byte. A start point ID has a word size.  


For example, to read seven data points in a double word format, i.e. 14 words, starting with point 0x0C00 (V1-V3, I1-I3, kW L1, see p.12 in the PM130 PLUS PROFIBUS Reference Guide), write the master request as follows:      Byte 1 Byte 2 Byte 3 Byte 4  1 (0x01)  14 (0x0E)  12 (0x0C)  0 (0x00)   The first byte contains a READ command (0x01), the second byte requests reading of 14 words (0x0E), and bytes 3 and 4 specify the start point address of 0x0C00.  


The following screenshots show how the master PLC request is written to its output buffer and how the meter response appears in the master input buffer. All data is given in a hexadecimal notation.





 The first four bytes of the response just repeat the master request "010E0C00" and the following bytes contain requested data, each point four bytes (32 bits) long, high order bytes first:   Bytes 5-8 (V1): "0000048A" in hex, or 1162 decimal. The meter PT ratio is set 1.0, so (see Section 4 in the PM130 PROFIBUS guide) the voltage unit is 0.1V and the actual V1 reading is 116.2V.

Bytes 9-12 (V2): "0000048A" in hex, or 1162 decimal, so the actual V2 reading is 116.2V.

Bytes 13-16(V3): "0000048C" in hex, or 1164 decimal, so the actual V3 reading is 116.4V ... an so on.