Host Computer Serial
To ensure reliable communication, it is essential to install an RS422/485 communications driver on the host computer For optimal protection against lightning damage and enhanced signal immunity to noise interference, it is highly advisable to choose an interface equipped with galvanic isolation.
OPTO22 Boards for use with
Where a personal computer is used as the host computer, the following OPTO22 boards are recommended for use with the COMMANDER 350 and 360 series of instruments:
AC24 AT AT Bus IBM PC compatible
Two-wire and Four-wire
Modbus serial communications require configuration as either two-wire or four-wire serial links, as illustrated in Figures 2.1 and 2.2 It is essential to select the appropriate two-/four-wire operation in the Configuration Mode, detailed in Section 3.1.
Fig 2.1 Pull-up and Pull-down Resistors (Two-wire Operation)
Pull-up and Pull-down
To avoid false triggering of slave devices when the master computer is inactive, it is essential to install pull-up and pull-down resistors on the RS422/485 interface of the host computer, as illustrated in Figures 2.1 and 2.2.
Termination Resistor
For long transmission lines, a 120Ω termination resistor must be fitted to the last slave in the chain – see Fig 2.3.
Fig 2.2 Pull-up and Pull-down Resistors (Four-wire Operation)
Serial Connections
• Up to 10 slaves can be connected to a single RS422 adaptor card on a PC.
• Up to 32 slaves can be connected to a single RS485 adaptor card on a PC.
The number of slaves can be increased if the driver's serial port permits.
To establish connections to the Modbus serial board, refer to Figs 2.1, 2.2, or 2.4 for guidance In systems with multiple slave devices, ensure that connections are made in parallel as depicted in Fig 2.3 Additionally, when connecting cable screens, take care to avoid introducing any 'ground loops.'
The maximum serial data transmission line length for both RS422 and RS485 systems is 1200m The types of cable that can be used are determined by the total line length:
Up to 6m – standard screened or twisted pair cable.
Up to 300m – twin twisted pair with overall foil screen and an integral drain wire, e.g Belden 9502 or equivalent.
Up to 1200m – twin twisted pair with separate foil screens and integral drain wires, e.g Belden
Press and hold Set the correct password
•1 COMMANDER 351 or COMMANDER 355 with ramp/soak disabled.
•2 COMMANDER 360 or COMMANDER 355 with ramp/soak enabled.
• Programmable baud rate – 2400, 9600 or 19200 baud.
• Selectable parity – odd, even or none.
For Modbus communications to operate correctly, each COMMANDER 350 or 360 must be configured with the correct serial transmission parameters and assigned a unique address.
Accessing the Serial
Fig 3.1 Access to Serial Configuration Displays
Setting the Serial
Note To select this frame from anywhere in this page, press the key for a few seconds.
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• The COMMANDER 350 and 360 operate as Modbus, Remote Terminal Unit (RTU) slaves.
• Parity checking – detects transmission errors in individual characters.
• Cyclic redundancy checking – detects errors in the master messages and slave responses.
Introduction
Modbus communication uses the master/slave principle to send messages to one or more slaves. Each slave is given a unique identity address (between 1 and 99).
A broadcast address (address zero) can be used to write to all slave devices simultaneously, using one command In this instance there is no slave acknowledgment.
Slaves are unable to receive new messages until they have processed the current one and sent a reply to the master, with a maximum response time of 125 milliseconds The slave tracks the time elapsed since the last character was received, and if this duration exceeds 3.5 character times, it interprets the next character as the beginning of a new message.
Note Modbus RTU requires 1 start bit, 8 data bits, 1 parity bit (optional) and 1 or 2 stop bits.
Modbus Function Codes
The function code instructs the addressed slave which function to perform Table 4.1 shows the function codes, and describes the action they initiate.
This section shows typical examples of Modbus function codes 01, 03, 05, 06, 08, 15 and 16.
Read Coil Status –
This function retrieves the ON/OFF status of logic coils that manage discrete outputs from the specified slave device Note that broadcast mode is not applicable for this function code The information field must include both the initial coil offset address and the quantity of locations to be queried, in addition to the slave address and function fields.
Note The coil offset address is one less than the coil number, e.g to start at coil 10 the start address must be set to 09 (09H).
Example Read 16 coils from slave (01) starting at coil 10 (alarm state 1).
Data is organized with one bit per coil, where 1 indicates ON and 0 indicates OFF Each response features the slave address, function code, data character count, the actual data characters, and error checking The first character's low order bit represents the first addressed coil, with subsequent coils following in order For quantities of coils that aren't multiples of eight, the remaining characters are padded with zeros at the high order end.
Read Holding Register –
The Read Holding Register Query obtains the contents of up to eight holding registers in the addressed slave.
Note The data start register must contain the offset address of the first register to be accessed, e.g to start at register 1 the data start register must contain 00 (00H).
Broadcast mode is not supported by Function Code 03.
Example Read two holding registers from slave (01) starting at holding address 01 (process variable input).
The addressed slave replies with its address and function code, followed by an information field that specifies the number of data bytes to be returned Each requested register is represented using two bytes, where the first byte holds the high order bits and the second byte contains the low order bits.
Force Single Coil –
This message forces a single coil either ON or OFF The data value 65,280 (FF00 HEX) sets the coil
ON and the value zero turns it OFF All other values are illegal and have no effect on coil status.
Note To write to a coil its offset address (one less than the coil number) must be used, e.g. to write to coil 39, the coil address 38 (26H) is transmitted.
The use of slave address zero (broadcast mode) forces all attached slaves to modify the desired coil.
Example Switch ON coil address 39 (auto/manual state) in slave 01.
The response is confirmation of the query after the coil state has been altered.
Preset Single Register –
The Preset Single Register Query modifies the contents of a holding register.
Note Function codes 05, 06, 15 and 16 are the only messages that are recognized as valid for broadcast.
Example Write the value 500 to holding register address 104 (proportional band 1 – heat) in slave 01.
Note To write to a register, its offset address (one less than the register number) must be used, e.g to write to register 104, the offset address 103 (67H) is transmitted.
The response to a Preset Single Register Response request is to retransmit the query message after the register has been altered.
Loopback Test –
The Loopback Test Query evaluates the Modbus system without impacting the slave's operation Any variations in the response may signal faults within the Modbus system The information field comprises two bytes for the diagnostic code, followed by two bytes indicating the required action.
The Loopback Test Response always echoes the query, only diagnostic code 0 (bytes 3 and 4) can be used.
Force Multiple Coils –
This message enables the simultaneous control of up to 32 coils, allowing them to be switched ON or OFF When employing a slave address of zero in broadcast mode, all slave controllers will adjust the designated coils to the specified states.
Note To write to a coil, its offset address (one less than the register number) must be used, e.g to write to coil 39, the offset address 38 (26H) is transmitted.
Example Force coil 39 to ON (Select manual mode) and coil 40 to OFF (Select Local Set Point mode).
The Force Multiple Coils Response confirms slave identification, function code, starting register address and quantity only.
H Low High Low High Low High Low
Write Multiple Registers –
This message enables the modification of up to eight holding registers simultaneously In broadcast mode, when utilized with slave address zero, all slave controllers update the designated registers with the specified contents.
Note To write to a register, its offset address (one less than the register number) must be used, e.g to write to register 104, the offset address 103 (67H) is transmitted.
Example Write the value 500 to the register address 104 (proportional band 1 – heat) and the value
100 to the register address 105 (integral action time) in slave 01.
The Write Multiple Registers Response confirms slave identification, function code, starting register address and quantity only.
The exception response codes from the slave, detailed in Table 6.1, are triggered when an error is detected Upon encountering such errors, the slave communicates with the master by sending a response message that includes the slave address, function code, error code, and error check fields.
Examples
A Read Register Request to read holding register address 300 of Slave 01 (undefined address for Slave, beyond address limit).
When a slave device encounters an 'illegal data address', it responds with an exception code that indicates an error This response is marked by setting the most significant bit of the function code to 1, signaling that an issue has occurred.
C VariableLabel Read/Write Limits/Values
Coils
C VariableLabel Read/Write Limits/Values
Single Loop Parameters (Templates 1 and 2)
Feedforward Parameters (Templates 9 and 10)
7 Slaveoutput1(heat) R/W* 0to1000(representing0.0to100.0%) 7
7 Slaveoutput2(cool) R/W* 0to1000(representing0.0to100.0%) 8
5 Slaveoutput1(heat) R/W* 0to1000(representing0.0to100.0%) 0
6 Slaveoutput2(cool) R/W* 0to1000(representing0.0to100.0%) s e u l a v t n i o p t e s l a c o l e h t o t e t i r w e u l a v t n i o p t e s e g n a h c o
Cascade with Feedforward Parameters (Template 13)
Control Monitor
1 Cycletime1 R/W 1.0to300.0or0.9(on/off)
1 Cycletime2 R/W 1.0to300.0or0.9(on/off)
1 Heat/cooloutput1start R/W 0to1000(representing0.0to100.0%) 9
1 Heat/cooloutput2start R/W 0to1000(representing0.0to100.0%) r e t s i g e
Set Point Parameters
Alarm Parameters
Motorized Valve Parameters
Basic Configuration
Math Blocks
Ramp/Soak Program Parameters (COMMANDER 355 and 360
Note On the instrument display, programs 10 to 20 are represented by the letters A to L(excluding I).
5 Segment1StartValue R/W 0to9999inengineeringunits,nodp.
9 Soaktimeadjustvalue R/W 0to1000,representing0.0to100.0in d e t c e l e s s t i n u e m i t 7
R RorR/W 1to20Programs or or or or o r onlywhenrun/hold
Ramp/Soak Segment
• AC and DC Drives, AC and DC Machines,
• Single and Multi-loop Controllers
• Circular Chart , Strip Chart and Paperless
• Industrial Robots and Robot Systems
• pH, conductivity, and dissolved oxygen transmitters and sensors
• ammonia, nitrate, phosphate, silica, sodium, chloride, fluoride, dissolved oxygen and hydrazine analyzers
• Zirconia oxygen analyzers, katharometers, hydrogen purity and purge-gas monitors, thermal conductivity
ABB Automation provides a comprehensive after sales service via our Worldwide Service Organization. Contact one of the following offices for details on your nearest Service and Repair Centre.
ABB Automation Limited Tel: +44 (0)1480-475-321 Fax: +44 (0)1480-217-948
Before installation, ensure that the equipment is stored in a clean, dry environment following the Company's specifications Regular inspections of the equipment's condition are essential.
In the event of a failure under warranty, the following documentation must be provided as substantiation:
1 A listing evidencing process operation and alarm logs at time of failure.
2 Copies of operating and maintenance records relating to the alleged faulty unit.