Micromod 2050R User Manual

MODBUS Communications for User’s Guide
MODCELL 2050R Supplement
Indicating Process Controller
2050R Model B Version 2.8 2051R Model B Version 2.8
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IB-23C650M

CONTENTS

CONTENTS
Page
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
About This Supplement . . . . . . . . . . . . . . . . . . . . . . 1
About Modbus Communications . . . . . . . . . . . . . . . . 1
Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Controller Option Requirements . . . . . . . . . . . . . . . . 3
2-Wire Modbus Network Connections . . . . . . . . . . . . 3
4-Wire Modbus Network Connections . . . . . . . . . . . . 5
Communication Applications . . . . . . . . . . . . . . . . . . . . . . 9
Standard Control with Modbus Communications . . . . 9
Supervisory Control . . . . . . . . . . . . . . . . . . . . . . . . 9
Computer Control . . . . . . . . . . . . . . . . . . . . . . . . . . 10
RS-485 Communications Setup . . . . . . . . . . . . . . . . . . . 11
Basic Operation With a Host Device . . . . . . . . . . . . . . . . 27
Enabling Write Communication With a Host . . . . . . . 27
Standard Communication With a Host . . . . . . . . . . . . 27
Supervisory Station . . . . . . . . . . . . . . . . . . . . . . . . . 29
Computer Auto/Manual Station . . . . . . . . . . . . . . . . . 30
Diagnostic Messages . . . . . . . . . . . . . . . . . . . . . . . 31
Modbus Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Communications Speed . . . . . . . . . . . . . . . . . . . . . . 33
Message Response Time . . . . . . . . . . . . . . . . . . . . 33
Messages Supported . . . . . . . . . . . . . . . . . . . . . . . 34
Message Formats . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Controller Attribute Listing - Register Data . . . . . . . . . . . . 39
Common Data (registers) . . . . . . . . . . . . . . . . . . . . 39
Ramp/Soak Profile and Totalizer Data (registers) . . . . 42
Tuning Parameter Data (registers) . . . . . . . . . . . . . . 44
Alarm Data (registers) . . . . . . . . . . . . . . . . . . . . . . . 46
Computer Activity Data (registers) . . . . . . . . . . . . . . 47
Ramp/Soak Profile Configuration Data (registers) . . . . 49
More Computer Activity Data (registers) . . . . . . . . . . 51
Controller Attribute Listing - Coil Data . . . . . . . . . . . . . . . 55
Computer Activity Data (coils) . . . . . . . . . . . . . . . . . 55
Digital Input and Output Data (coils) . . . . . . . . . . . . . 56
Ramp/Soak Data (coils) . . . . . . . . . . . . . . . . . . . . . . 57
i
IB-23C650M
CONTENTS
CONTENTS (Cont’d)
Page
Totalizer Data (coils) . . . . . . . . . . . . . . . . . . . . . . . . 57
Autotune Data (coils) . . . . . . . . . . . . . . . . . . . . . . . . 57
Process Alarm Data (coils) . . . . . . . . . . . . . . . . . . . . 58
Diagnostic Data (coils) . . . . . . . . . . . . . . . . . . . . . . . 59
Ramp/Soak Profile Data (coils) . . . . . . . . . . . . . . . . . 60
Record of Database . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
ILLUSTRATIONS
Figure Page
1 Typical 2-Wire Modbus Network Connections . . . . . . 4
2 Typical 4-Wire Modbus Network Connections with . . . 6 a Host Device as Master 3 Typical 4-Wire Modbus Network Connections with . . . 7 a MODCELL Multiloop Processor as Master
TABLES
Table Page
1 RS-485 Setup Menu . . . . . . . . . . . . . . . . . . . . . . . . 12
2 Modbus Messages Supported by MODCELL 2050 . . . 35
ii
IB-23C650M

INTRODUCTION

INTRODUCTION About This Supplement
This supplement provides instructions for installation, setup, and use of the Modbus RS-485 serial communications option available in the MODCELL 2050 Single Loop Controller. Comprehensive instructions covering all aspects of the controller not related to Modbus communication are included in the
IB-23C650 User’s Guide.
Specific information provided in this supplement is as follows:
• Instructions for connecting the controller to a Modbus network using either a 2-Wire or 4-wire configuration.
• Application information including controller operation as a supervisory station or computer auto/manual station using Modbus communications.
• Step-by-step instructions for setup of the communications function using the RS-485 MENU in the controller data base.
• Operating instructions for the controller when Modbus communication with a host device is enabled.
• A description of the Modbus messages supported and the message formats.
• Controller attribute reference data. The listing includes register data for numeric attributes and coil data for boolean (discrete) attributes.
About Modbus Communications
A 2050R controller and a host device connected to a Modbus network communicate via a master/slave relationship. The host device functions as the Modbus master and the controller functions as the slave. The master is in command of the communications transaction and talks to one slave (controller) at a time. The master sends a message to a slave and waits to receive an answer back from that slave before it talks to the another slave. Each slave has a unique address which
1
IB-23C650M
INTRODUCTION
allows it to be identified by the master. This permits multiple slaves (controllers) to reside on a single Modbus network.
The controller can be assigned any address between 1 and 247. Addresses are set in the RS-485 MENU as part of the setup for modbus communication. Address 0 is the “broadcast” address. Only write messages can use it. All controllers process the message, but there is no response back to the host.
Other types of slaves may reside on a network with the controllers. Modbus does not support peer-to-peer communications where two controllers can talk directly with each other.
2
IB-23C650M

INSTALLATION

INSTALLATION
This section provides instructions for making Modbus network connections using either a 2-wire or 4-wire configuration. This information assumes that physical installation and all other electrical connections are being made in accordance with the instructions in IB-23C650.
Before making any connections, be sure the controller can support Modbus communications; see the option requirements below.
Controller Option Requirements
The controller must be equipped with an option card and firmware Version 2 to run MODBUS RS-485 serial communications. The option card (Catalog No. 2050NZ10100A) and Version 2 firmware may have already been installed in the controller during manufacture. If necessary these items can be installed in the field. Instruments manufactured with the option card and Version 2 firmware are identified by digits in the instrument catalog number as shown below:
Sample Catalog Number: 2050RZ10 1 02 A RS-485 Communications Option Card RS-485 Firmware Version
2-Wire Modbus Network Connections
Connections for a typical Modbus network using a 2-wire configuration are shown in Figure 1. The host device functions as the master and the controllers function as slaves. It is recommended that no more than 32 devices be connected on a single network. The devices and host must have a common ground.
The master is responsible for providing the 560 ohm pull-up and pull-down bus stabilizing resistors. Connect 120 ohm termination resistors across the transmission line at both ends as shown. The number of devices can be increased by the use of repeaters. The termination resistors may not be required if the line length is very short.
Cable requirements depend on the length of the run. For short runs of 10 to 25 ft (3 to 6m) virtually any 2-wire shielded or twisted pair is suitable. For runs up to 4000 ft (1219m) Belden 9841 cable or equivalent is recommended. This cable is a 24 AWG twisted pair with a foil shield. The insulation is low dissipation (polypropylene). A drain wire is provided for grounding the shield.
3
IB-23C650M
INSTALLATION
Personal Computer Modbus Master
RS485 Interface
+5V dc
560
All resistors are 0.25W.
Other 2050R's
wired same way
without resistors.
RX/TX+
120
RX/TX-560
COM
120
RX+
RX -
TX+
TX -
COM
Last
2050R
Figure 1. Typical 2-Wire Modbus Network Connections
.
4
IB-23C650M
INSTALLATION
4-Wire Modbus Network Connections
Connections for typical Modbus networks using a 4-wire configuration are shown in Figures 2 and 3. The host device functions as the master and the controllers function as slaves. It is recommended that no more than 32 devices be connected on a single network. The number of devices can be increased by the use of repeaters.
When the host is a device such as a personal computer, the instruments and host must have a common ground as shown in Figure 2. When the host is a MODCELL Multiloop Processor, Figure 3, connection of the processor to the instrument common line is not required because the processor connections are optically isolated.
The master is responsible for providing the 560 ohm pull-up and pull-down bus stabilizing resistors. In the MODCELL processor, these resistors are provided in the RS-485 communications module, and the TERM switch on the module must be set at YES to connect the resistors to the network (see IB-23C600 MODCELL Multiloop Processor Installation Instructions for more information). Connect 120 ohm termination resistors across the transmission line at both ends as shown. The termination resistors may not be required if the line length is very short.
Cable requirements depend on the length of the run. For short runs of 10 to 25 ft (3 to 6m) virtually any 2-wire shielded or twisted pair is suitable. For runs up to 1000 ft (305m), Belden 9502 cable or equivalent is recommended. This cable is a dual 24 AWG twisted pair with an overall foil shield. A drain wire is provided for grounding the shield. For runs up to 4000 ft (1219m) Belden 9729 or equivalent is recommended. This cable is a dual 24 AWG twisted pair with a foil shield for each pair. The cable insulation is low dissipation (polypropylene). Two separate drain wires are provided for grounding the shields.
5
IB-23C650M
INSTALLATION
Personal Computer Modbus Master
RS485 Interface
+5V dc
560
560
560
560
2050R Controller
(Modbus Slave)
All resistors are 0.25W.
Other 2050R's
wired same way
without resistors.
RX+
120
RX-
TX+
120
TX-
COM
120
120
RX+
RX -
TX+
TX -
COM
Figure 2. Typical 4-Wire Modbus Network Connections with a Host
Device as Master
6
Last
2050R
IB-23C650M
INSTALLATION
Modcell Processor
Isolated +5Vdc
560
TERM
Switch
YES
Modbus Master
2034N RS-485 MODULE (Module Locations 31 & 32)
2050R Controller
(Modbus Slave)
S31
1
2
S32
1
2
All resistors are 0.25W.
Other 2050R's
wired same way
without resistors.
RX+
120
RX-
TX+
120
TX-
120
120
RX+
RX -
TX+
TX -
COM
2050R
Figure 3. Typical 4-Wire Modbus Network Connections with a
MODCELL Multiloop Processor as Master
Last
7
IB-23C650M
INSTALLATION
Blank Page
8
IB-23C650M

COMMUNICATION APPLICATIONS

COMMUNICATION APPLICATIONS
The following are sample applications available with the controller through the use of Modbus communications. The RS-485 MENU is used to set up the controller for these applications. The setup requirements are described in detail in Table 1.
Standard Control With Modbus Communications
For this application, the instrument acts as a stand alone single loop controller which can receive read/write commands from a host Modbus device such as a personal computer, MODCELL Multiloop Processor, PLC, etc. Multiple instruments and other devices can be on a single Modbus network. Each device on a network must have a unique address. The instrument address is assigned using the Bus Address attribute in the RS-485 MENU.
During runtime operation, the last attribute entry to the controller becomes the active entry. For example, if the operator sets an active set-point value via the instrument display and moments later the host sends a new active set-point value, the controller uses the operators value until it receives the host value. At that time the host value becomes the new active set-point value.
A prompt in the DISPLAYS MENU permits the operator to disable the host from writing to the controller. The host can still receive data from the instrument, but can not write to it. This is useful if the operator must maintain manual control of the process and does not want the host to write to the instrument. The operator can reinitiate the host write capacity via the DISPLAYS MENU when required.
The Computer Timeout attribute is not active in this application. When necessary, this attribute is initialized by the host as a means of notifying the instrument of a communication failure. In this application, failure of the host or the communications has no effect on instrument operation. The controller continues to operate with its current attribute values as if nothing happened.
Supervisory Control
The controller receives its set-point from the host device in a supervisory control application. All other aspects of controller operation are similar to standard control as described above. The PID control function is provided by the controller.
9
IB-23C650M
COMMUNICATION APPPLICATIONS
Attributes in the RS-485 MENU permit the supervisory control mode to be indicated via the set-point status display on the front of the instrument. Each of the three characters in the status display is configurable so that the user can choose an appropriate mnemonic to represent the supervisory control mode.
A timeout value can be defined for communications traffic to the instrument via the Computer Timeout attribute. An activity timer in the instrument is initialized by the host when operation starts. This action also enables the configured set-point status display.
The timer monitors the communications bus for activity to the instrument within the specified timeout period. If there is no communications activity to the instrument during the specified time, a "computer failure" is declared. During a computer failure the controller assumes local control with I/O and mode states as defined under "Computer Failure Setup" in the RS-485 MENU.
When the controller is receiving a set-point from the host, the set-point status display can be configured to indicate that the host is the set-point source. The R/L key still performs its normal function. The set-point status display indicates changes in the set-point source ( LOC, LO1, etc. ).
Computer Control
In a computer control application, the instrument functions as a computer auto/manual station. The host performs the PID control function with the results communicated to the controller and then to the field.
Attributes in the RS-485 MENU permit the computer control mode to be indicated via the control and set-point status displays on the front of the instrument. Each of the three characters in each status display is configurable so that the user can choose appropriate mnemonics to represent the computer control mode and set-point status.
A computer timeout value is defined and a timer monitors communications in the same manner as for supervisory control. When the computer is active, the function of the AUTO, R/L and Maunal keys can be configured to provide a signal to the computer upon which it can take some programmed action.
10
IB-23C650M
RS-485 COMMUNICATIONS SETUP
RS-485 COMMUNICATIONS SETUP
Before starting the communications setup, refer to the Setup Section in IB-23C650 for information about the setup preparation, method, and controls.
Perform the communications setup using the RS-485 MENU as described in Table 1.
Note: In order to access the RS-485 MENU, the RS-485 Communications
Enable attribute in the BASE CONFIGURATION MENU must be set at YES. Refer to Table 1, Base Configuration in IB-23C650.
11
IB-23C650M
RS-485 COMMUNICATIONS SETUP
Table 1. RS-485 Setup Menu
Step Step Description
1
2
3
4
5
RS-485 Menu. (requires option board)
UP
moves to RELAYS **MENU**.
DN
moves to RAT BIAS **MENU** if A/M ratio bias
is enabled, or to SETPTS **MENU** otherwise.
SCRL
advances to Step 2 (read only in auto).
Bus Enable
UP
or
DN
selects ON or OFF.
SCRL
to advance to Step 3.
Instrument Address
UP
or
DN
sets instrument address.
SCRL
to advance to Step 4.
Baud Rate
UP
or
DN
sets instrument baud rate.
SCRL
to advance to Step 5.
Parity Selection
UP
or
DN
sets instrument parity.
SCRL
to advance to Step 6.
Top
Display
RS-485
BUS
BUS
BAUD
PARITY
6
7
12
Stop Bit Selection
UP
or
DN
sets number of stop bits.
SCRL
to advance to Step 7.
Allowed Access Type
UP
or
DN
sets communications access type.
SCRL
to advance to Step 8.
STOP
ACCESS
RS-485 COMMUNICATIONS SETUP
Table 1. RS-485 Setup Menu
IB-23C650M
Middle
Display
**MENU**
ENABLE ON
Bottom Display
Entry Description
None.
= enables the bus for communications with a host device. = disables the communications bus from
OFF
receiving or writing with a host device. The bus must be disabled in order to make changes in the following steps.
ADDRESS XXX Where X is any address between 1 and 247.
Each instrument on a bus must have a unique address.
RATE XXXX Where X is one of the following baud rates;
150, 300, 1200, 2400, 4800, 9600, 19200,
38400. All devices on the same bus must have the same baud rate.
SELECT
ODD EVEN
BITS 1
= Parity calculation is odd. = Parity calculation is even. Note: Total word length equals start bit (1) + data (8 bits) + parity (1) + stop bits (1/2). Total word length can be 11 or 12 bits.
= One stop bit appended to character.
2
= Two stop bits appended to character.
TYPE RD_ONLY
RD/WRITE
= Allows the host device to read only from the controller. = Allows the host device to read data from and write data to the controller.
13
IB-23C650M
RS-485 COMMUNICATIONS SETUP
Table 1. RS-485 Setup Menu
Step Step Description
8
8.1
8.2
Computer Activity Setup.
UP
begins setup at Step 8.1.
SCRL
to advance to Step 9 (Enable Bus).
Computer Activity Timeout.
UP
or
DN
sets value.
SCRL
to advance to Step 8.2.
Computer Activity Mnemonic (Auto )
UP
or
DN
sets value (press
press
UP
to start at A or press
Press
SCRL
to access the next character.
Repeat through the third character. Press after the third character to continue with step 8.3.
UP
to begin then
DN
to start at 9 ).
Top
Display
COMPUTER
COMPUTER
CMP AUTO
SCRL
8.3
14
Computer Activity Mnemonic (Manual)
UP
or
DN
set values and characters as described in Step 8.2. Press after the third character to continue with step 8.4.
SCRL
accesses
SCRL
CMP MAN
RS-485 COMMUNICATIONS SETUP
Table 1. RS-485 Setup Menu
IB-23C650M
Middle
Display
SETUP
Bottom Display
Entry Description
Steps 8.1 through 8.12.6.1.1allow setup for the controller to be used as a computer auto/manual (CAM) or supervisory station when connected to a host device. No entries are required if the instrument is to be used as a stand alone controller which can receive read/write commands from a host device.
TIMEOUT XXXXX X represents a time between 1 and 16383
seconds. The computer activity timeout function is initialized and maintained by the computer (host). If the time between sessions of bus activity is greater than this value, a Computer Fail is declared. This causes the activity timer to be disabled, and the computer status reverts to LOCKED. The controller returns to local with parameters as defined in Step 8.12.
MNEMONIC XXX Where X = any of the following characters:
Letters A through Z, Any of the special characters:
b, c, super c, d, h, sub L, super L, super m, super n, o, r, super T, u, super V, w, <, >, =, +, –, *, #, /, %, degrees (super o), or space,
Numbers 0 through 9. Mnemonic appears in the control mode status display when the activity timer is initialized by the host and control mode is automatic. Default mnemonic is CMP.
MNEMONIC XXX Where X = any of the characters listed in
Step 8.2 Mnemonic appears in the control mode status display when the activity timer is initialized by the host and control mode is manual. Default mnemonic is MAN.
15
IB-23C650M
RS-485 COMMUNICATIONS SETUP
Table 1. RS-485 Setup Menu
Step Step Description
8.4.
8.5
8.6
Computer Control Mode Value
UP
or
DN
sets value.
SCRL
to advance to Step 8.5
Computer Set-point Mnemonic (Local)
UP
or
DN
sets value (press
press
UP
to start at A or press
Press
SCRL
to access the next character.
Repeat through the third character. Press after the third character to continue with Step 8.6.
Computer Set-point Mnemonic (Local 2)
UP
or
DN
set values and characters as described in Step 8.5. Press after the third character to continue with Step 8.7.
UP
SCRL
to begin then
DN
to start at 9.
accesses
Top
Display
COMPUTER
CMP LOC
SCRL
CMP LO2
SCRL
8.7
16
Computer Set-point Mnemonic (Local 3)
UP
or
DN
set values and characters as described in Step 8.5. Press after the third character to continue with Step 8.8.
SCRL
accesses
SCRL
CMP LO3
RS-485 COMMUNICATIONS SETUP
Table 1. RS-485 Setup Menu
IB-23C650M
Middle
Display
MODE VAL XXX
Bottom Display
Entry Description
Where X = any value between 0 and 255. This value is OR'd into bits 9-12 of the Control Mode register (#14) when the activity timer is enabled. Default value is 1.
MNEMONIC XXX Where X = any of the following characters:
Letters A through Z, Any of the special characters:
b, c, super c, d, h, sub L, super L, super m, super n, o, r, super T, u, super V, w, <, >, =, +, –, *, #, /, %, degrees (super o), or space,
Numbers 0 through Mnemonic appears in the set-point status display when the activity timer is initialized by the host and set-point source is local, or when coil #8 is True and the computer set-point mode is Local. Default is LOC.
MNEMONIC XXX Where X = any of the characters listed in
Step 8.5. Mnemonic appears in the set-point status display when the activity timer is initialized by the host and set-point source is Local 2. Default is LO2.
MNEMONIC XXX Where X = any of the characters listed in
Step 8.5. Mnemonic appears in the set-point status display when the activity timer is initialized by the host and set-point source is Local 3. Default is LO3.
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