Satec ETC2002 User manual

ETC2002
Modbus Communications Protocol
Reference Guide
©SATEC Ltd.
BG0367 Rev. A2

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Every effort has been made to ensure that the material herein is complete and accurate.
However, the manufacturer is not responsible for any mistakes in printing or faulty instructions
contained in this book. Notification of any errors or misprints will be received with
appreciation.
For further information regarding a particular installation, operation or maintenance of
equipment, contact the manufacturer or your local representative or distributor.
Modbus is a trademark of Modicon, Inc.

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Table of Contents
1GENERAL ...................................................................................................5
2MODBUS PROTOCOL IMPLEMENTATION...............................................6
2.1 Transmission Modes..................................................................................................6
2.2 Address Field.............................................................................................................6
2.3 Function Field............................................................................................................6
2.4 Exception Responses................................................................................................6
2.5 Modbus Register Addresses .....................................................................................6
2.6 Data Formats.............................................................................................................7
2.7 Password Protection..................................................................................................7
3DATA SERVER...........................................................................................8
3.1 Data Server Features ................................................................................................8
3.2 Using Real-time Data Exchanges..............................................................................9
3.2.1 Configuring Real-time Data Exchanges..................................................................................9
3.2.2 Accessing Real-time Data Exchanges....................................................................................9
3.2.3 Accessing Data Log Files .....................................................................................................10
3.3 Using Status Event Exchanges and Event Logs.....................................................11
3.3.1 Configuring Event Exchanges...............................................................................................11
3.3.2 Accessing the Event Log File................................................................................................11
3.4 Using Data Write Exchanges...................................................................................12
4MODBUS REGISTER MAP.......................................................................13
4.1 Data Server Registers .............................................................................................13
Real-time Data Exchange Block................................................................................13
Data Write Exchange Block.......................................................................................13
Data Log Transfer Blocks..........................................................................................13
Event Log Transfer Blocks.........................................................................................14
4.2 Digital Inputs............................................................................................................14
4.3 Device Control and Status Registers.......................................................................15
Device Mode Control Registers (factory set).............................................................15
Device Diagnostics Register (bit map) ......................................................................15
Device Authorization Register ...................................................................................15
Factory Diagnostic Registers.....................................................................................15
4.4 Device Setup Registers...........................................................................................15
Factory Device Settings and Identification ................................................................15
Device Options Setup................................................................................................16
Time/Date Setup........................................................................................................16
Clock Setup and Status.............................................................................................16
Modem Setup ............................................................................................................17
Communication Ports Setup......................................................................................17
Network Setup ...........................................................................................................17
RF Modem Setup.......................................................................................................17
Password Setup.........................................................................................................18
Expert Power Service Setup......................................................................................18
Internet Service Provider (ISP) Accounts..................................................................18
Data Server Setup.....................................................................................................18
Gateway Setup ..........................................................................................................19
Device Routing Table ................................................................................................20
Routing IP Table........................................................................................................20

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5DATA FORMATS ......................................................................................21
Timestamp.................................................................................................................21
Event Type ID............................................................................................................21
Event Data.................................................................................................................21
Device Diagnostics (bitmap)......................................................................................21
Shared Access Rules ................................................................................................22

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1 General
This document specifies a subset of the Modbus serial communications protocol used to transfer data
between a master computer station and the ETC2002. The document provides the complete
information necessary to develop third-party communications software capable of communication
with the ETC2002. Additional information concerning communications operation, configuring the
communications parameters, and communications connections is found in "ETC2002 Installation and
Operation Manual".
IMPORTANT
Most of the advanced features are configured using multiple setup parameters that can be accessed in a
number of contiguous registers. When writing the setup registers, it is recommended to write all the registers
at once using a single request.

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2 Modbus Protocol Implementation
For detailed information about Modbus protocol, Modbus message framing and error checking, refer
to the "Modicon Modbus Protocol Reference Guide". It can be downloaded from the Modicon's Web
site at www.modicon.com. The following paragraphs outline some issues concerning the
implementation of the Modbus protocol in the ETC2002.
2.1 Transmission Modes
The ETC2002 can be set up to communicate on a Modbus network using ASCII or RTU transmission
mode. Refer to the "ETC2002 Installation and Operation Manual " on how to select the transmission
mode in your device.
2.2 Address Field
The address field contains a user assigned address of the instrument (1-247) on a Modbus network.
Broadcast mode using address 0 is not supported.
2.3 Function Field
The Modbus functions implemented in the ETC2002 are shown in Table 2-1. Function 04 can be used
in the same context as function 03.
Table 2-1 Modbus Function Codes
Code (decimal) Meaning in Modbus Action
03 Read holding registers Read multiple registers
04 Read input registers Read multiple registers
06 Preset single register Write single register
16 Preset multiple registers Write multiple registers
081Loop-back test Communications test
1The ETC2002 supports only diagnostic code 0 - return query data.
2.4 Exception Responses
The instrument sends an exception response when an error is detected in the received message. To
indicate that the response is notification of an error, the high order bit of the function code is set to 1.
Implemented exception response codes:
1 - Illegal function
2 - Illegal data address
3 - Illegal data value
10 - Gateway is busy. Remote access is temporarily unavailable.
When the character framing, parity, or redundancy check detects a communication error, processing of
the master's request stops. The instrument will not act on or respond to the message.
2.5 Modbus Register Addresses
The ETC2002 Modbus registers are numbered in the range of 0 to 65535. From the Modbus
applications, the ETC2002 Modbus registers can be accessed by simulating holding registers of the
Modicon 584, 884 or 984 Programmable Controller, using a 5-digit “4XXXX” or 6-digit “4XXXXX”
addressing scheme. To map the ETC2002 register address to the range of the Modbus holding
registers, add a value of 40001 to the ETC2002 register address. When a register address exceeds 9999,
use a 6-digit addressing scheme by adding 400001 to the ETC2002 register address.

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2.6 Data Formats
The ETC2002 uses two data formats to pass data between a master application and the device: 16-bit
short integer and 32-bit long integer formats. Data logged by the ETC2002 Data Server is collected
from instruments in 16-bit short integer format.
2.7 Password Protection
The ETC2002 has a password protection option allowing you to protect your setups and logs from
being changed or cleared through communications. You can disable or enable password protection
through communications or via the Terminal. For details, refer to the ETC2002 “Installation and
Operation Manual”. When password protection is enabled, the user password you set in the ETC2002
should be written into the device authorization register (44378-44379) before another write request is
issued. If the correct password is not supplied while password protection is enabled, the ETC2002 will
respond to all write requests with the exception code 01 (illegal operation). It is recommended to clear
the password register after you have completed your changes in order to activate password protection.

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3 Data Server
3.1 Data Server Features
The Data server allows the user to save the time required for polling multiple devices, especially via
slow serial interfaces, by utilizing the ETC2002 non-volatile memory for automatic acquiring data. The
user application can then read blocks of ready data directly from the ETC2002 memory without the
need to wait until slow devices respond to master requests. The Data server can also perform a delayed
write of data so the application needs not to wait until the device would be accessible, but rather can
write data to the ETC2002 memory exchanges, and then the ETC2002 takes responsibility for
delivering data to the target devices. The Data server can also periodically poll device status registers
and record events to a log file or give alerts on specific events.
The following table lists the configurable Data server options.
Table 3-1 Data Server Options
Description Range
Data server enabled 1=enabled, 0=disabled
Continuous polling 1=enabled, 0=disabled
Data polling interval 1-1000 min
Data logging interval, polls 0-1000, 0=logging disabled
When the Data server is enabled, it acquires data from the connected devices either continuously, or
on a periodic basis. If continuous polling is disabled, the devices are requested periodically at
predefined poll intervals. If continuous polling is enabled, the ETC2002 retrieves data from the devices
in turn without pauses.
Acquired real-time data is normally stored in the ETC2002 exchanges (memory blocks) and is
periodically refreshed at programmed intervals. The ETC2002 provides up to 250 real-time data
exchanges of 1 to 114 registers long. These exchanges can be directly accessed by the master
application.
If the user wishes, acquired data can be periodically moved to historical circular files where it will be
kept for a long time until it is overwritten by newer data. Data is stored to historical files at regular
intervals. The logging interval is always represented as a whole number of data polling intervals even if
the polling itself is not synchronized with polling intervals like in the event of continuous polling. Since
the ETC2002 tries to synchronize polling devices with the beginning of an hour, it is recommended to
program a logging interval in such a manner that it would be a whole divisor of 60 minutes. Historical
records can be accessed one record at a time either in an arbitrary order, or in a sequential manner.
The ETC2002 also provides up to 250 write data exchanges, of 1 to 12 registers long, and up to 250
status event data exchanges of 1 register long. Table 3-2 gives a summary of the available data
exchanges.
Table 3-2 Data Server Exchanges
Exchange Type Number of
Exchanges Exchange Block Size, registers
Real-time data exchange 250 1-114
Status event exchange 250 1
Data write exchange 250 1-12
NOTE:
The real-time, status event and write data exchanges with the same exchange number are internally
linked in the ETC2002 to the same device ID. If you change the device ID for one of the
exchanges, the same ID will be taken for other configured exchanges that have the same exchange
number.

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3.2 Using Real-time Data Exchanges
3.2.1 Configuring Real-time Data Exchanges
Real-time data exchanges are used for periodic retrieving data from the connected devices. The
following table shows the parameters that should be configured before enabling a data exchange.
Table 3-3 Real-time Data Exchange Setup
Description Range
Exchange number 0-249
Start device register address 0-65535
Exchange block size, registers 1-114
Device ID 1-247
Polling enabled 1=enabled, 0=disabled
RTC update enabled (optional) 1=enabled, 0=disabled
A data exchange can store from 1 to 114 contiguous 16-bit registers retrieved from a single device. A
block of registers for an exchange is defined by the start register address and the exchange block size.
Refer to Modbus guides for specific devices for available address ranges.
You can individually enable or disable polling data for a specific exchange. If the device has an
onboard real-time clock, you can enable periodic RTC updates from the ETC2002 clock, which may
be synchronizes with the precise satellite GPS clock using an optional IRIG-B input.
Each data exchange utilizes 6 extra registers for time stamping and identification as shown in
Table 3-4, so the actual memory required for one data exchange is 6 + exchange block size. The total
size of all exchanges should not exceed 9000 registers.
Table 3-4 Data Exchange Record
Description Range
Record heading
Record status 0=no data, -1=corrupted record,
1-65534 = device response code
Record time, seconds since 1/1/1970
Record sequence number 0- 65535
Data block (variable size)
Data registers (up to 114)
If data logging is globally enabled in the Data server, the retrieved data is periodically moved from the
data exchange to a log file in the same format, as it is stored in the exchange (see Table 3-4). Each
exchange is provided with a separate data log file.
A data record is always preceded by a status register that indicates whether the data is healthy. Each
record may be identified in a file by a unique 16-bit sequence number that is incremented modulo
65536 with each new record.
3.2.2 Accessing Real-time Data Exchanges
Real-time data exchanges occupy a single continuous block of registers without gaps and are located in
the ETC2002 memory in the address range of 0 to 9000. Since exchanges may have different size, the
location of each exchange in the memory depends on the size of all preceding exchanges. Use the
following formula to define the location of the data exchange:
)6SizeBlockExchange(AddressExchange 1N
0n nN +
∑
=
−
=
Note that a location of the exchange in the memory is changed when you change the data exchange
setup, so the previously acquired data would be lost.

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3.2.3 Accessing Data Log Files
Each data exchange is provided with a separate circular data log file. The Data server allocates a total
of 1.5 Mbytes of non-volatile memory for all data log files, which will be equally divided between all
active exchanges.
File transfers are performed through two blocks of registers: a master request block and a read-only file
transfer block, which are shared by all files. After a master application has written the request with a
file exchange number (and possibly a file position) into the file request block, the requested data is
available for a read through the file transfer block registers. File transfer functions allow changing the
file position in order to point to the desired record in a selected log file. The sequence number of the
first (oldest) record available in a file may be inspected via the file request block after the file exchange
number is written into the block.
The file transfer block occupies 120 registers in the address range of 9000 to 9119. The following table
shows a layout of the data log request block. Refer to Table 3-3 for the file transfer block layout.
Table 3-5 Data Log Request Block
Description Range
Function 3 = set file position
5 = reset file position
11 = read record
Record sequence number (with functions 3, 11) 0-65535
First (oldest) record sequence number 0-65535
Exchange number 0-249
Data log files can be read either in a sequence record-by-record, or in a random order. Every write to
the file request block fills the file transfer block with the data of the record pointed to by the file read
pointer. If you want to begin reading a file from a particular record, which sequence number is known,
you can change the pointer position by issuing the Set-File-Position request with the desired sequence
number. If you want to read a file from the beginning, write the Reset-File-Position request that moves
the pointer to the oldest file record. If you use the Read-Record request that does not change the file
position, then you will continue reading the file from the record following the one you have read the
last time you accessed the file.
You need not explicitly move the file position to the following record if you want to continue reading a
file in sequence after you have uploaded the current record. Instead, continue reading the record data
through the file transfer block: each access to the file transfer block automatically advances the file
pointer to the next record. That’s why you should read all data in the file transfer block by a single
request: the next read will give you the following file record.
The file transfer is completed after you have read the last record of the file. Before storing a file record
to your database, always check the record status word. This word set to 0 indicates that the file read
pointer does not point to any record within the file, and you should not store any record that has this
word set to 0 or to -1.
The following gives a summary of steps you should perform to read a data log file:
1) If you want to begin reading a file from a particular record or from the first record, use either the
Set-File-Position request with the desired record sequence number, or the Reset-File-Position
request; otherwise use the Read-Record request.
2) Read the record data from the file transfer block. The file pointer will be moved to the next file
record.
3) Repeat step 2 until all the file records are read, i.e., until the record status word indicates the end-
of-file.