CARLO GAVAZZI EM21 - COMMUNICATION PROTOCOL V1 REV0, EM21, EM24 DIN Communication Protocol Manual

EM21

COMMUNICATION

PROTOCOL

Version 1 Revision 0

April 7th, 2008

Index

1.1 Introduction ...........................................................................................................................................3

1.2 MODBUS functions...............................................................................................................................3

1.2.1 Function 03h (Read Holding Registers) ..............................................................................3

1.2.2 Function 04h (Read Input Registers) ..................................................................................4

1.2.3 Function 06h (Write Single Holding Register) .....................................................................4

1.2.4 Function 08h (Diagnostic with sub-function code 00h)........................................................5

1.2.5 Broadcast mode ..................................................................................................................5

1.3 Application notes...................................................................................................................................6

1.3.1 RS485 general considerations ............................................................................................6

1.3.2 MODBUS timing..................................................................................................................6

2 TABLES.........................................................................................................................................7

2.1 Data format representation In Carlo Gavazzi instruments ....................................................................7

2.1.1 Geometric representation....................................................................................................7

2.2 Maximum and minimum electrical values in EM21 ...............................................................................7

2.3 Instantaneous variables and meters.....................................................................................................8

2.4 Firmware version and revision code ..................................................................................................... 8

2.5 Programming lock status.......................................................................................................................8

2.6 Carlo Gavazzi Controls identification code ........................................................................................... 9

2.7 Programming parameter tables.............................................................................................................9

2.7.1 Password configuration menu.............................................................................................9

2.7.2 “Application” menu...............................................................................................................9

2.7.3 System configuration menu.................................................................................................9

2.7.4 PT and CT configuration menu............................................................................................9

2.7.5 Pulse output configuration menu.......................................................................................10

2.7.6 Serial port configuration menu...........................................................................................10

2.7.7 Reset commands...............................................................................................................10

2.7.8 Note...................................................................................................................................10

3 REVISIONS..................................................................................................................................10

Energy management

EM24-DIN Communication Protocol

3

1.1 Introduction

The RS485 serial interface supports the MODBUS/JBUS (RTU) protocol. In this document only the
information necessary to read/write from/to EM21 has been reported (not all the parts of the protocol
have been implemented).
For a complete description of the MODBUS protocol please refer to the
“Modbus_Application_Protocol_V1_1a.pdf” document that is downloadable from the www.modbus.org
web site.

1.2 MODBUS functions

These functions are available on EM21:

• Reading of n “Holding Registers” (code 03h)

• Reading of n “Input Register” (code 04h)

• Writing of one “Holding Registers” (code 06h)

• Diagnostic (code 08h with sub-function code 00h)

• Broadcast mode (writing instruction on address 00h)

IMPORTANT:

1) In this document the “Modbus address” field is indicated in two modes:

1.1) “Modicom address”: it is the “6-digit Modicom” representation with Modbus function code 04
(Read Input Registers). It is possible to read the same values with function code 03 (Read
Holding Registers) replacing the first digit (“3”) with the number “4”.

1.2) “Physical address”: it is the “word address” value to be included in the communication

frame.

2) The functions 03h and 04h have exactly the same effect and can be used indifferently.

3) The communication parameters are to be set according to the configuration of the instrument
(refer to EM21 instruction manual)

1.2.1 Function 03h (Read Holding Registers)
This function is used to read the contents of a contiguous block of holding registers (word). The Request

frame specifies the starting register address and the number of registers to be read. It is possible to
read maximum 11 registers (words) with a single request, when not differently specified.
The register data in the response message are packed as two bytes per register (word), with the binary
contents right justified within each byte. For each register, the first byte contains the high order bits
(MSB) and the second contains the low order bits (LSB).

Request frame

Description Length Value Note

Physical address 1 byte 1 to F7h (1 to 247)
Function code 1 byte 03h
Starting address 2 bytes 0000h to FFFFh Byte order: MSB, LSB
Quantity of registers (N word) 2 bytes 1 to 10h (1 to 11) Byte order: MSB, LSB
CRC 2 bytes

Response frame (correct action)

Description Length Value Note

Physical address 1 byte 1 to F7h (1 to 247)
Function code 1 byte 03h
Quantity of requested bytes 1 byte N word * 2
Register value N*2 bytes Byte order: MSB, LSB
CRC 2 bytes