ABB DATUM L150 User manual

ABB Instrumentation
DATUM L150/160 Operating Guide
MODBUS (RTU)
Communications Option
DATUML150
888888
A1
A2
A3
888888
DATUML160

Note.
Clarification of an instruction or
additional information.
Information.
Further reference for more detailed
information or technical details.
Use of Instructions
Although Warning hazards are related to personal injury, and Caution hazards are
associated with equipment or property damage, it must be understood that operation of
damaged equipment could, under certain operational conditions, result in degraded
process system performance leading to personal injury or death. Therefore, comply fully
with all Warning and Caution notices.
Informationinthismanualisintendedonlytoassistourcustomersintheefficientoperation
of our equipment. Use of this manual for any other purpose is specifically prohibited and
its contents are not to be reproduced in full or part without prior approval of Technical
Communications Department, ABB Instrumentation.
Health and Safety
To ensure that our products are safe and without risk to health, the following points
must be noted:
1. The relevant sections of these instructions must be read carefully before
proceeding.
2. Warning labels on containers and packages must be observed.
3. Installation, operation, maintenance and servicing must only be carried out by
suitably trained personnel and in accordance with the information given.
4. Normal safety precautions must be taken to avoid the possibility of an accident
occurring when operating in conditions of high pressure and/or temperature.
5. Chemicalsmustbestoredawayfromheat,protectedfromtemperatureextremes
and powders kept dry. Normal safe handling procedures must be used.
6. When disposing of chemicals ensure that no two chemicals are mixed.
Safety advice concerning the use of the equipment described in this manual or any
relevant hazard data sheets (where applicable) may be obtained from the Company
address on the back cover, together with servicing and spares information.
Warning.
An instruction that draws attention to
the risk of injury or death.
Caution.
An instruction that draws attention to
the risk of damage to the product,
process or surroundings.

1
CONTENTS
1 INTRODUCTION ........................................................................................... 2
2 ELECTRICAL INSTALLATION .................................................................... 3
2.1 Host Computer Serial Communications............................................... 3
2.2 OPTO22 Boards for use with Personal Computers............................. 3
2.3 Two-wire and Four-wire Connection .................................................... 3
2.4 Pull-up and Pull-down Resistors .......................................................... 6
2.5 Termination Resistor ............................................................................ 6
2.6 Serial Connections ............................................................................... 6
3 CONFIGURATION ........................................................................................ 8
3.1 Accessing the Configuration Mode ...................................................... 8
3.2 Setting the Serial Transmission Parameters ....................................... 8
3.3 Setting the MODBUS Address ............................................................. 8
4 MODBUS PROTOCOL ................................................................................. 9
4.1 Introduction ........................................................................................... 9
4.2 MODBUS Function Codes.................................................................. 10
5 MODBUS FUNCTIONS............................................................................... 11
5.1 Read Coil Status – Function Code 01 ............................................... 11
5.2 Read Holding Register – Function Code 03 ...................................... 12
5.3 Force Single Coil – Function Code 05 ............................................... 13
5.4 Preset Single Register – Function Code 06 ...................................... 14
5.5 Loopback Test – Function Code 08 ................................................... 15
5.6 Write Multiple Registers – Function Code 16 .................................... 16
6 EXCEPTION RESPONSES ........................................................................ 17
6.1 Examples ............................................................................................ 17
7 ADDRESSABLE PARAMETERS............................................................... 18
7.1 Coils ............................................................................................... 18
7.2 Registers ............................................................................................. 18
7.2.1 Analog Inputs ........................................................................ 18
7.2.2 Alarm Settings....................................................................... 19
7.2.3 Maths Functions.................................................................... 19

2
1 INTRODUCTION
This Operating Guide describes the DATUM L150/L160 MODBUS serial data
communications option and must be used in conjunction with the standard
User
Guide
( IM/L150 or IM/L160 ) supplied with the instrument.
Information.
The MODBUS option provides the following facilities:
• Standard RS422/485 communications.
• MODBUS RTU protocol – for master (host computer) to slave
(DATUM L150/L160) system.
• 500V d.c. isolation from external connections to the instrument.
• Two-wire or four-wire communication.
• 2400 or 9600 baud transmission rate.
• Parity-checking – odd, even or none.

3
2 ELECTRICAL INSTALLATION
This section describes the connection of serial data transmission cables between
the master (host computer) and slave DATUM L150/L160 instruments on a
MODBUS serial link. All connections other than those used for serial
communication are shown in Section 5 of the relevant
User Guide .
2.1 Host Computer Serial Communications
An RS422/485 communications driver must be fitted to the host computer. It is
strongly recommended that the interface has galvanic isolation to protect the
computer from lightning damage and increase signal immunity to noise pick-up.
2.2 OPTO22 Boards for use with Personal Computers
Where a personal computer is used as the host computer, the following OPTO22
boards are recommended for use with the DATUM L150/L160 Series of
instruments:
Part No. Computer Type
AC24 AT AT Bus IBM PC compatible
AC34 Microchannel IBM PC
2.3 Two-wire and Four-wire Connection – Figs. 2.1 and 2.2
MODBUSserialcommunicationsmustbeconfigured as either two-wire or four-wire
seriallinks – seeFigs. 2.1 and2.2. Two-/Four-wire operationmust also beselected
in the Configuration Mode – see Section 3.1.

4
…2 ELECTRICAL INSTALLATION
2.4 Pull-up and Pull-down Resistors – Figs. 2.1 and 2.2
To prevent false triggering of slaves when the master (host computer) is inactive,
pull-upandpull-down resistors must be fittedtotheRS422/485interface in the host
computer – see Figs. 2.1 and 2.2.
+5V
0V
1.8kΩPull-up
Resistor
1.8kΩPull-down
Resistor
Host Computer
Rx–
Rx+
Tx–
Tx+
'A'
'A
'B'
'B
GND
20
21
22
23
24
Tx+/Rx+
Tx–/Rx–
GND
+5V
0V
1.8kΩPull-up
Resistor
1.8kΩPull-down
Resistor
Host Computer
Rx–
Rx+
Tx–
Tx+
'A'
'A
'B'
'B
GND
Tx+/Rx+
Tx–/Rx–
GND
11 12 13
Fig. 2.1b Two-wire Operation – L160
Fig. 2.1a Two-wire Operation – L150

5
2 ELECTRICAL INSTALLATION…
…2.4 Pull-up and Pull-down Resistors
Host Computer
+5V
0V
'A 'B
1.8kΩ
Pull-down
Resistor
1.8kΩPull-up
Resistor
0V
+5V
0V
'A
'B
1.8kΩ
Pull-down Resistor
1.8kΩ
Pull-up
Resistor
Rx+
Rx–
Tx–
Tx+
GND
20
21
22
23
24
Fig. 2.2a Four-wire Operation – L150
Fig. 2.2b Four-wire Operation – L160
Host Computer
+5V
0V
'A 'B
1.8kΩ
Pull-down
Resistor
1.8kΩPull-up
Resistor
0V
+5V
0V
'A
'B
1.8kΩ
Pull-down Resistor
1.8kΩ
Pull-up
Resistor
Rx+
Rx–
Tx–
Tx+
GND
9 10 11 12 13

6
…2 ELECTRICAL INSTALLATION
2.5 Termination Resistor – Fig. 2.3
For long transmission lines, a 120Ωtermination resistor must be fitted to the last
slave in the chain – see Fig. 2.3.
First
S
lave Last
S
lave
Tx+
Tx-
Rx+
Rx-
GND
120Ω
Termination Resistor
(External)
M
as
t
er
Rx+
Rx–
Tx+
Tx–
GND
Tx+
Tx–
Rx+
Rx–
GND
Host
Computer
Fig. 2.3 Connecting Multiple Slaves
2.6 Serial Connections – Figs. 2.1 to 2.4
Information.
• 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.
Connections to the MODBUS serial board must be made as shown in Figs. 2.1, 2.2
or 2.4. Connections on links with multiple slaves must be made in parallel, as
shown in Fig. 2.3. When connecting cable screens, ensure that no 'ground loops'
are introduced.
Themaximum serial datatransmission line length forboth 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 9729 or equivalent.

7
2 ELECTRICAL INSTALLATION
…2.6 Serial Connections – Figs. 2.1 to 2.4
Rx+
Rx–
Tx+
GND
Rx+
Rx–
Tx+
Tx–
GND
OPTO22 Adaptor
Board Connections
Screen
Tx– 8
9
4
5
3
Fig. 2.4 OPTO22 Board Connections

8
3 CONFIGURATION
Fig. 3.1 Setting Serial Transmission Parameters
Information.
• Programmable baud rate – 2400 or 9600 baud.
• Selectable parity – odd, even or none.
• Address range – 1 to 99.
For MODBUS communications to operate correctly, each DATUM L150/L160 must
be configured with the correct serial transmission parameters and assigned a
unique address.
3.1 Accessing the Configuration Mode
The procedure for accessing the Configuration Mode is detailed in Section 4.2 of
the relevant
User Guide. When all parameters have been programmed, return the
instrument to the Operator Mode.
3.2 Setting the Serial Transmission Parameters – Fig. 3.1
Fig. 3.1 shows the display readouts and options available when defining the serial
transmission rate and bit parity for DATUM L150/L160 instruments. Further detail
on the procedures required to set each parameter are shown in Section 4.3 of the
relevant User Guide.
3.3 Setting the MODBUS Address
To allow the master to differentiate between more than one slave in a system, each
slave on a MODBUS link must be assigned a unique address in the range 1 to 99
– see Section 4.4 of the relevant
User Guide (MODBUS Address Frame, Addr).
Display Parity
0 None
1Odd
2 Even
S 0000t 0000
S – Serial Communication Configuration T – Serial Communications Parity
Display Baud Rate, 2/4-wire
0Off
1 2400, 2-wire
2 2400, 4-wire
3 9600, 2-wire
4 9600, 4-wire

9
4 MODBUS PROTOCOL
Information.
• The DATUM L150/L160 operates as a MODBUS, Remote Terminal Unit
(RTU) slave.
• Parity checking – detects transmission errors in individual characters.
• Cyclic redundancy checking – detects errors in the master messages and
slave responses.
4.1 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 cannot accept new messages until the current message has been
processed and a reply sent to the master (maximum response time 250ms). The
slave monitors the elapsed time between receipt of characters. If the elapsed time
without a new character is 31/2character times, the slave assumes the next
character received is the start of a new message.
Note. MODBUS RTU requires 1 start bit, 8 data bits, 1 parity bit
(optional) and 1 or 2 stop bits.

10
…4 MODBUS PROTOCOL
4.2 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.
*NAK = Negative Acknowledgment
Table 4.1 MODBUS Function Codes
Function
Code Function Title Description
01 Read
Coil Status Read up to 16 consecutive discrete (Boolean) points from a specific starting point. The DATUM L150/L160
returns zeros for points which do not contain defined
data and NAKs* any request for point numbers
greater than 60.
Read up to 8 consecutive registers from a specific
starting register. The DATUM L150/L160 returns
zeros for points which do not contain defined data
and NAKs* any request for point numbers greater
than 90.
Write one discrete (Boolean) point. The DATUM
L150/L160 NAKs* this if the point is not currently
writeable.
Write one register. This code also applies any
existing limits to the register before storage in the
instrument. The DATUM L150/L160 NAKs* if the
register is not currently writeable.
Echo the message. Only 'Return of Query' is
supported.
Write up to eight consecutive registers from a
specified starting register. The DATUM L150/L160
NAKs* if any of the registers are not currently
writeable, but carries out all the writes which are
valid, applying any existing limits to the value before
storage in the instrument.
03 Read
Holding Register
05 Force
Single Coil
06 Preset
Single Register
08 Loop Back
16 Preset
Multiple
Registers

11
This section shows typical examples of MODBUS function codes 01, 03, 05, 06, 08
and16.Notall addressable parameters used in theexamples whichfollowarevalid
for both instrument types – see Sections 7.1 and 7.2.
5.1 Read Coil Status – Function Code 01
5.1.1 Read Coil Status Query
This function obtains the ON/OFF status of logic coils used to control discrete
outputs from the addressed slave. Broadcast mode is not supported with this
function code. In addition to the slave address and function fields, the information
fieldmust contain theinitialcoil offset address(starting address) and thenumber of
each location to be interrogated.
Note. The coil offset address is one less than the coil number, e.g. to
start at coil 06 the start address must be set to 05 (05H).
Example –read 16 coils from slave (01) starting at coil 6 (alarm state 1).
Address Function Coil Start Coil Start No. of No. of Error Check (CRC-16)
Offset High Offset Low Coils High Coils Low Field
01 01 00 05 00 10 2D C7
5.1.2 Read Coil Status Response
The data is packed one bit for each coil (1 = ON, 0 = OFF). The response includes
the slave address, function code, quantity of data characters, the data characters
and error checking. The low order bit of the first character contains the first
addressed coil and the remainder follow. For coil quantities that are not multiples of
eight, the last characters are packed with zeros at the high order end.
Example:
Alarms 1, 2 and 3 inactive
Digital input inactive
Digital output inactive
Relays 1 and 2 active
ON/OFF status 1 and 2 active
Data Coil Data Coil Error Check (CRC-16)
Address Function Byte Count Status Status Field
6 to 13 14 to 21
01 01 02 00 3E 38 2C
5 MODBUS FUNCTIONS

12
5.2 Read Holding Register – Function Code 03
5.2.1 Read Holding Register Query
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 three holding registers from slave (01) starting at holding address
01 (process variable input).
Register Register Data No. Data No. Error
Address Function Start Start of Registers of Registers Check (CRC-16)
Offset High Offset Low High Low Field
01 03 00 00 00 03 05 CB
5.2.2 Read Holding Register Response
The addressed slave responds with its address and function code, followed by the
information field. The information field contains one byte describing the quantity of
data bytes to be returned. Two bytes are used to return each register requested,
the first byte containing the high order bits and the second the low order bits.
Example:
PV input (two registers) – 270
PV decimal places – 1
Byte Holding Holding Holding Error
Address Function Count Register 01 Register 02 Register 03 Check (CRC-16)
High Low High Low High Low Field
01 03 00 00 00 01 09 00 01 49 75
…5 MODBUS FUNCTIONS

13
5 MODBUS FUNCTIONS…
5.3 Force Single Coil – Function Code 05
5.3.1 Force Single Coil Query
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 30, the coil address 29 (1CH) is transmitted.
The use of slave address zero (broadcast mode) forces all attached slaves to
modify the desired coil.
Example –switch ON coil address 30 (auto/manual state) in slave 01.
Coil Coil Data Data Error
Address Function Offset Offset Value Value Check (CRC-16)
High Low High Low Field
01 05 00 1D FF 00 80 FF
5.3.2 Force Single Coil Response
The response is confirmation of the query after the coil state has been altered.
Example:
Coil Coil Data Data Error
Address Function Offset Offset Value Value Check (CRC-16)
High Low High Low Field
01 05 00 1D FF 00 28 60

14
…5 MODBUS FUNCTIONS
5.4 Preset Single Register – Function Code 06
5.4.1 Preset Single Register Query
The Preset Single Register Query modifies the contents of a holding register.
Note. Function codes 05, 06 and 16 are the only messages that are
recognized as valid for broadcast.
Example –write the value 500 to holding register address 25 (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 register25, the offsetaddress 24 (18H)
is transmitted.
Register Register Data Data Error
Address Function Offset Offset Value Value Check (CRC-16)
High Low High Low Field
01 06 00 18 01 F4 09 DA
5.4.2 Preset Single Register Response
The response to a Preset Single Register Response requests is to retransmit the
query message after the register has been altered.
Example
Register Register Data Data Error
Address Function Offset Offset Value Value Check (CRC-16)
High Low High Low Field
01 06 00 18 01 F4 09 DA

15
5 MODBUS FUNCTIONS…
5.5 Loopback Test – Function Code 08
5.5.1 Loopback Test Query
The Loopback Test Query tests the MODBUS system and does not affect the
operation of the slave. Variations in the response may indicate faults in the
MODBUS system. The information field contains two bytes for the designation of
the diagnostic code followed by two bytes to designate the action to be taken.
Example:
Data Data Error
Address Function Diagnostic Diagnostic Data* Data* Check (CRC-16)
Code High Code Low Field
01 08 00 00 A5 37 DA 8D
*These are considered to be the information fields for the diagnostic mode.
5.5.2 Loopback Test Response
The Loopback Test Response always echoes the query, only diagnostic code 0
(bytes 3 and 4) can be used.
Example:
Data Data Error
Address Function Diagnostic Diagnostic Data Data Check (CRC-16)
Code High Code Low Field
01 08 00 00 A5 37 DA 8D

16
…5 MODBUS FUNCTIONS
5.6 Write Multiple Registers – Function Code 16
5.6.1 Write Multiple Registers Query
This message is used to change the contents of up to eight holding registers at a
time. When used with slave address zero (broadcast mode) all slave controllers
load the selected registers with the contents specified.
Note. To write to a register, its offset address (one less than the register
number)must be used, e.g. to write to register25, the offsetaddress 24 (18H)
is transmitted.
Example –write the value 500 to the register address 25 (proportional band 1 –
heat) and the value 100 to the register address 26 (integral action time) in slave 01.
Register Register Number of Byte
Address Function Start Start Registers Count
Offset High Offset Low
01 10 00 18 00 02 04
Holding Holding Holding Holding Error Check
Register 24 Register 24 Register 25 Register 25 Field (CRC16)
High Low High Low
01 F4 00 64 B2 E0
5.6.2 Write Multiple Registers Response
TheWriteMultipleRegistersResponseconfirmsslaveidentification,functioncode,
starting register address and quantity only.
Example:
Register Register Number of Error
Address Function Start Offset Start Offset Registers Check (CRC-16)
High Low Field
01 10 00 18 00 02 C1 CF

17
6.1 Examples
A Read Register Request to read holding register address 100 of Slave 01
(undefined address for Slave, beyond address limit).
Register Register Number Number Error
Start Start of of Check
Address Function Offset Offset Registers Registers Field (CRC-16)
High Low High Low
01 03 00 FA 00 06 E5 F9
Theslavereplies with an exceptionresponsesignifyingan 'illegal data address'.To
indicate that the response is a notification of an error, the most significant bit of the
function code is set to 1.
Slave Address Function Exception Error Check (CRC-16)
01 83 02 C0 F1
6 EXCEPTION RESPONSES
Table 6.1 Exception Response Codes
The exception response codes sent by the slave are shown in Table 6.1. When a
slave detects one of these errors, it sends a response message to the master
consisting of slave address, function code, error code and error check fields.
Exception
Response
Code
Exception Response
Name Exception Response Definition
Illegal
Function
Illegal
Data Address
Illegal
Data Value
Negative
Acknowledgement
Memory
Parity Error
The message function received is not an allowable
function on the COMMANDER 100/150.
The address reference in the data field is not an
allowable address for the COMMANDER 100/150.
The value referenced in the data field is not allowable
in the addressed slave location.
The function just requested cannot be performed.
Parity check indicates an error in one or more of
the characters received.
01
02
03
07
08

18
7.1 Coils
Coil No. Variable Label Read/Write Limits/Values
1 Process Variable Fail State R 1 = Failed
3 A/D Converter Fail State R 1 = Failed
6 Alarm State 1 R 1 = Active
7 Alarm Indicator 1 R 1 = On
8 Alarm State 2 R 1 = Active
9 Alarm Indicator 2 R 1 = On
10 Alarm State 3 R 1 = Active
11 Alarm Indicator 3 R 1 = On
14 Digital Input State R 1 = On
15 Digital Output State R 1 = On
16 Relay 1 State R 1 = On
17 Relay 2 State R 1 = On
21 Global Maths Reset W 1 = Reset
22 Maximum Values Reset W 1 = Reset
23 Minimum Values Reset W 1 = Reset
24 Average Values Reset W 1 = Reset
7.2 Registers
7.2.1 Analog Inputs
Register Variable Label Read/Write Limits/Values
1 + 2 Process Variable Input R –9999 to 99999
3 PV Decimal Places R 0 to 4
4 + 5 Specific Gravity R/W –999.9 to 9999.9
5 + 6 Volume R –999.9 to 9999.9
7 ADDRESSABLE PARAMETERS