Passive REST Client to Modbus RTU/TCP, BACnet IP Gateway (discontinued)

The Passive REST Client (XML, JSON, CSV) to Modbus RTU/TCP, BACnet IP Gateway acts as a protocol converter. It allows Passive REST Client (XML, JSON, CSV) devices to communicate with devices on a BACnet IP network.
The BACnet IP Driver allows the Gateway to transfer data to and from devices over Ethernet UDP/IP using the BACnet IP protocol.
The Modbus TCP Driver allows the FieldServer to transfer data to and from devices over Ethernet using the Modbus TCP Protocol.
Modbus Serial over RS232 or RS485. We have all variants of this protocol.
SKU:
CAS2700-35
CAS gateway 800 BLACK no Background - CAS gateway 800

The Passive REST Client Gateway receives REST requests containing data in XML, JSON, or CSV format. This data can contain most data types (character strings, floating point values, binary values, etc). The Gateway then serves the data as BACnet IP data points.

The Gateway receives REST requests on its Web Server port. The data is then parsed and stored internally. When a remote system requests data, this data is served in a form that is appropriate to the protocol.

The Gateway requires configuration for setting up the serving tasks to make BACnet IP data points.

The Gateway requires configuration for setting up the serving tasks to make Modbus RTU/TCP data points.

CAS Hardware 700

The CAS 700 Hardware device contains 2x 9-pin serial ports (1x RS485 and 1xRS232), and one Ethernet port. The device also contains a microSD card where system files, assets, configurations, and logs are stored.

The device has the following system drivers that can be enabled:

  • HTTP REST Server - a passive web server with an API that users can interact with the device to get or set values
  • HTTP Push Driver - a driver that can be configured to push data in a specific format (JSON, XML, CSV) to a 3rd party web server. Current data formats are Chipkin's default JSON payload and VeederRoot Tank data as JSON. Please contact Chipkin for information on adding additional formats.

Modbus TCP

The Modbus TCP Driver allows the FieldServer to transfer data to and from devices over Ethernet using Modbus TCP Protocol. The Modbus TCP driver uses port 502. This port is not configurable. The driver was developed for Modbus Application Protocol Specification V1.1a" from Modbus-IDA. The specification can be found at www.modbus.org. The FieldServer can emulate both a Client and a Server simultaneously on the same ethernet port.

The information that follows describes how to expand upon the factory defaults provided in the configuration files included with the FieldServer.

There are various register mapping models being followed by various vendors. To cover all these models FieldServer uses the following three Models

  • Modicon_5digit – Use this format where addresses are defined in 0xxxx, 1xxxx, 3xxxx or 4xxxx format. A maximum of 9999 registers can be mapped of each type. This is FieldServer driver’s default format.
  • ADU –Application Data Unit address. Use this format where addresses of each type are defined in the range 1-65536
  • PDU –Protocol Data unit address. Use this format where addresses of each type are defined in the range 0-65535.

The key difference between ADU and PDU is for example if Address_Type is ADU and address is 1, the driver will poll for register 0. If Address_Type is PDU, the driver will poll for address 1.

Note 1: If vendor document shows addresses in extended Modicon (i.e. 6 digit) format like 4xxxxx then consider these addresses as xxxxx (omit the first digit) and use either ADU or PDU

Note 2: The purpose of providing 3 different ways of addressing the Modbus registers is to allow the user to choose the addressing system most compatible with the address list being used. At the protocol level, the same protocol specification is used for all three with the exception of the limited address range for Modicon_5digit.

Modbus RTU

The Modbus RTU driver allows our FieldServer gateways to transfer data to and from devices over either RS-232 or RS-485 using Modbus RTU protocol. The Gateways are capable of being used as port expanders and can emulate either a Server or Client. The FieldServer is capable of supporting devices that use two Modbus Registers to transfer IEEE floating point format.


The information that follows describes how to expand upon the factory defaults provided in theconfiguration files included with the FieldServer.


There are various register mapping models being followed by various vendors.


  • To cover all these models FieldServer uses the following three Models
  • Modicon_5digit – Use this format where addresses are defined in 0xxxx, 1xxxx, 3xxxx or 4xxxxformat. A maximum of 9999 registers can be mapped of each type. This is FieldServer driver’sdefault format.
  • ADU –Application Data Unit address. Use this format where addresses of each type are definedin the range 1-65536
  • PDU –Protocol Data unit address. Use this format where addresses of each type are defined inthe range 0-65535.

The key difference between ADU and PDU is for example if Address_Type is ADU and address is 1, thedriver will poll for register 0. If Address_Type is PDU, the driver will poll for address 1. 


BACnet IP Driver

The CAS BACnet IP driver allows the CAS Gateway to transfer data to and from devices over Ethernet UDP/IP using the BACnet IP protocol.  The CAS Gateway can either be a Client, reading and storing values from a BACnet device, or a Server, making data available as BACnet objects.

The CAS BACnet IP Driver supports the following BACnet Services:

- Who-Is- Who-Has
- Read Property- Read Property Multiple
- Write Property- Write Property Multiple
- Subscribe COV     - Time Synchronization

Note: Chipkin is always updating the BACnet IP Driver. For a recent list of supported services, please visit www.chipkin.com or contact us. If there are services that you require that are not listed, please contact us to discuss how we can add them to the driver.

I'd like to inquire about the Passive REST Client to Modbus RTU/TCP, BACnet IP Gateway (discontinued) CAS2700-35. Please provide me with a quote for this product.

Specifications

CAS Hardware 700

The following specifications are common to all Chipkin gateways.

  • Certifications: UL and ULc approved
  • Ports:
    • 10/100BASE-T with RJ-45 connector
    • 1x RS232 port
    • 1x RS485 port (different models have additional ports)
  • Power: 7 - 24 VDC through an external power supply. (12V @ 90mA)
  • Operating temperature: 0 - 70 °C (32 - 158 °F)
  • LEDs: link, speed/data, power

Dimensions
  • Dimensions (LxWxH): 107 x 83 x 25 mm (4.2 x 3.25 x 1 in.)
  • Connection type: RS485 (jumper change to RS232)

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Block Diagrams

imports/blockDiagrams/LP Modbus.jpg

Resources

All CAS 2500, 2700, 2800 products

A quick start guide with instructions for some of the basic operations of the CAS Gateway product line. Includes instructions for the following:

  • Detecting the CAS Gateway via the computer and settings its IP Address
  • Downloading the Firmware to the CAS Gateway
  • Downloading the Assets to the CAS Gateway
  • Downloading the Configuration to the CAS Gateway

Additional Information

Modbus - MK10 and 32 Bits Numbers

Scaling in Modbus

Modbus does not provide a method for transporting large or Floating Point numbers or a mechanism for scaling analog values. A 16 bit word can only contain values in the range 0-65535. Only whole numbers are permitted. To work around this many server device manufacturers use multipliers and document them in their manuals. For example, to report a temperature of 58.5 the device reports a value of 585, and makes a note in the manual that the master should scale by 10. This scaling is achieved by adopting a convention between the client and the server.
What about large numbers > 65535
Modbus does not provide a mechanism but 3 important schemes are widely used.

Long Integers – Two consecutive 16 bit words are interpreted as a 32 bit long integer.

MK10 values – Two consecutive words are used. The 1st reports the number of units and the 2nd reports the number of 10,000’s.

Floating Point Numbers – Two consecutive words are used and a scheme. These schemes are conventions and not all servers or clients support them.

The protocol does not identify these big numbers. Only the vendor docs do.
What we mean by this is – if you look at the byte stream in a Modbus message there is no way of telling whether you are looking at two consecutive 16 bit words, or two consecutive words that should be interpreted as floating point, long or MK10 formats. Because of this you always have to look to the vendor docs.

Modbus - Reading Vendor Modbus Maps

Reading Vendor Modbus Maps

 

If you are reading the documentation for sensor blocks, valves, and other devices, you must keep in mind that some vendors may document their hardware in different ways.

According to the Modbus standard, addresses are simply integers from 0 to 65,535 with the different address ranges being referred to as coils, holding registers, etc. However, some vendors will document their hardware using numerical prefixes which are not actually part of the Modbus address. This originated from some models of PLCs which used the Modbus communications protocol, and which also used numerical prefixes in their internal data table. This is similar to using “I”, “Q”, “V”, etc. as address prefixes in IEC type PLCs.

However, it is important to remember that these numerical prefixes are documentation methods and are not part of what the Modbus protocol itself sends as part of the messages. A difference in documentation methods does not affect the compatibility of the protocol itself.

These prefixes are they mentioned anywhere in the Modbus standard, but the following shows how they are typically used in documentation based on this older convention:

  • 0xxxx – Coils.
  • 1xxxx – Discrete inputs.
  • 3xxxx – Input registers.
  • 4xxxx – Holding registers.

Note that there is no 2xxxx address prefix.

In addition to numerical prefixes, some documentation will refer to protocol addresses (addresses start at 0), while other documentation will refer to data model addresses (addresses start at 1). That is, the first holding register may be 0 or 1 (or 40000 versus 40001 using prefixes). However, this has no bearing on what gets sent over the wire as a Modbus message. For a Modbus protocol message, the lowest address is always “0”, not “1”.

Modbus - Protocol Specifications
Modbus - Flavors of Modbus

Flavors of Modbus

RTU:

Common
Binary Protocol.
Active Master-passive Slave
Serial
Supported by FieldServers, QuickServers, CAS gateways

 

ASCII:

Similar to ModbusRTU but for each byte in an RTU message, there are 2 bytes in an ASCII message. The 2 bytes are the humand readable form of the single hex byte.
Eg RTU byte = 0x03 (Hex). ASCII bytes = ‘0’ and ‘3’ ie 0x30 and 0x33
Active Master-passive Slave
Serial
Supported by FieldServers, QuickServers

 

Jbus:

Modbus had the limitation of a max of 9999 items of each type. Ie only 9999 holding registers. However the protocol message allows 65k items to be addressed. JBUS allows all 65k items to be read/written. Other than that it is identical to RTU
Active Master-passive Slave
Serial
Supported by FieldServers, QuickServers, CAS gateways

 

TCP/IP:

Uses TCP/IP connection based Ethernet communications
Encapsulates RTU messages and adds a header.
A single slave can respond to multiple masters
Many slaves ignore the NodeID field in the message.
Supported by FieldServers, QuickServers, CAS gateways

 

MB Plus:

Proprietary coax networking layer
2 Mbits/sec
Supported by FieldServers, CAS gateways

Modbus for Field Technician - Free Booklet
ModbusRTU - ModbusTCP - Port Expansion

Port Expansion

FieldServer can easily be configured to allows a Modbus RTU client to talk to a ModbusTCP server and vice versa. You do not need to tell the FIeldServer which registers to map from one to the other. You simply configure the FieldServer telling it which port and protocol to use for each node.

 

In port expansion mode configuration can be moinimal. Tell the gateway which nodes are on which port and set the port settings.

ModbusRTU - Scaling and Bit Packing

Scaling / Bit Packing

FieldServers can scale data and manipulate values using some binary logic and arithmetic functions. Scaling can be applied to each block of Modbus Data read / served.

  • Move to change type : Convert from any FIeldServer Data Type to any other.
  • Move to pack/unpack bits and bytes: It’s possible to address each bit in a 8,16 or 32 bit data element by using the packed data types.
  • Move to change byte/word order: Handle the endianess of the remote system easily.
  • Convert to/from Float, MK10, IEE754, 32 bit, 16 bit, 8 bit numbers
  • Move conditionally:
  • Perform Arithmetic Operation: + – * div sqrt, sqr ,
  • Perform Binary Logic Operation: And, Or, Not, >, >= , <, <=

 

Most functions can be configured to occur on a configurable period or on update of the data source.

 

ModbusRTU - Supported Data Types

Supported Data Types

Bit

Byte

16 Bit Integer Signed

16 Bit Integer Unsigned

32 Bit Integer Signed

32 Bit Integer Unsugned

32 Bit Packed Bit

8 Bit Packed Bit

4 byte FLoating Point Numbers

ModbusRTU - Supported Functions

Supported Modbus Functions

01 Read Discrete Output Status (0xxxx)
02 Read Discrete Input Status (1xxxx)
03 Read Output Registers (4xxxx)
04 Read Input Registers (3xxxx)
05 Force Single Coil (0xxxx)
06 Preset Single Register (4xxxx)
15 Force Multiple Coils (0xxxx)
16 Preset Multiple Registers (4xxxx)

Articles

Table 2 Modbus Registers
Modbus - Convert between Modbus Flavors
How Real (Floating Point) and 32-bit Data is Encoded in Modbus RTU Messages
Modbus - C#
Modbus - Modhopper for Modbus Wireless Communication
Modbus - 32 bit numbers
Modbus - Multiple Masters of one slave
ModbusTCP - Modbus Transaction Identifier
Modbus - There are (were) a Max of 9999 points of each data type
ModbusTCP - What type of protocol is Modbus TCP
ModbusTCP - What do you have that can help me convert my Modbus TCP data
ModbusTCP - We want to check the communication between our device and personal computer, so we need the 232 communication software
Simplified Configuration for Modbus-to-Modbus Integration with Fieldserver Devices
ModbusTCP - Can you give me an example of a Modbus/TCP to BACnet/IP configuration
ModbusTCP - How can I use Modbus Scanner to Write Registers of Digitrip 3000 (Protective Relays) Controls
Modbus - What is Modbus? (extended article)
Modbus - What is the Modbus Transaction Identifier
Modbus - Can you give me a list of Useful tools and applications for Modbus
How to Make the CAS Modbus Scanner Read A Modbus 6 Digit Address (JBUS)
USING PUTTY OR REALTERM FOR SERIAL COM CONNECTIONS (HyperTerminal replacement)
Testing Modbus communication
Low Power Wireless Modbus
Modbus Frequently Asked Questions (FAQ) and Answers
FS-8704-03 – Modbus TCP
Modbus Protocol Specification
Modbus Specifications and Implementation Guides
MODBUS Exception Responses
Case Study - Modbus RTU and Veeder Root to Ethernet IP
Case Study - Modbus RTU (RS485) - BACnet MSTP Integration

Logos

Logo Modbus

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