Modbus is a messaging protocol that defines the content of that message.

In a short time hundreds of vendors implemented the Modbus messaging system in their devices and Modbus became the de facto standard for industrial communication networks.

Communication between the Modbus nodes was achieved with messages. It was an open standard that described the messaging structure. domain map The physical layer of the Modbus interface was free to choose.

The original Modbus interface ran on RS232, but most later Modbus implementations used RS485 because it allowed longer distances, higher speeds and the possibility of a true multi-drop network. RS485 is hardware serial-interface standard that defines the hardware for carrying a message.

If you need more info on MODBUS check this manual out!

DL3500 General Operation & Applications

DL3500 General Operation & Applications

The DL3500 continues the functionality of the DL2000/DL3000 product line. It offers both the new addition of DH485 as well as a plug and play USB interface. As well as having the DH+ and 232/422/485 capabilities of the DL3000. Two DL3500 Models will also allow Bridging between DH+ and DH485networks. New is the ability to power the DL3500 from the USB communication link, removing the sometimes cumbersome procedure of location an AC or DC power supply when using laptops or PC’s inthe field.

The DL3500 has two communication ports. Channel A is designed to connect to you industrial network,either AB DH+ or DH485 networks. Channel B is used to connect to your serial or USB device, the protocol depends on which flavour (model) of the DL3500 you have ordered.

Channel B has the capabilities of RS232C, RS422, RS485 and USB 2.0. Configuration of the operating parameters is done quickly and easily by the DL32 V3.X windows based software shipped with the unit or available on the Equustek Website. Currently there are three standard DL3500 products available to allow access to A-B’s DH-485 and DH+ network.

Many other custom ASCII and serial protocols have been implemented to Both DH+ and DH-485 on the DL3500 platform. Contact Equustek Solutions to see if the DL3500 is the correct device for your communication needs.

The DL3500 has all three models below available in DH+ and DH485 flavours:

The DL3500-Modbus is a two port device that bridges your Modicon Modbus devices to ones on an Allen Bradley DH485 or DH+ network. The Modbus model can either be used as Modbus Master or Modbus Slave as well as having both Modbus ASCII and RTU protocols.

The DL3500-DF1 is a two port device that allows your DF1 devices (either Full or Half Duplex protocols) to ones on an Allen Bradley DH485 or Allen Bradley DH+ network. The DF1 model is a direct replacement for the 1770-KF3 for DH-485 and 1770-KF2 for DH+ and allows your PCs or Laptops access to any node on the corresponding A-B network.

The DL3500-ASCII interfaces Serial ASCII devices (Scanners/Printers) to SLC’s or other devices on an Allen Bradley DH485 or DH+ network. The DL3500-DF1/DH+ or DH485 interfaces your DF1 devices (either Full or Half Duplex protocols) to ones on either an AB DH485 or DH+ network. The DL3500 comes with both networks available with only using the software configuration program to switch between the DH485 and DH+ networks


DL4000 General Operation & Applications

The DL4000 hardware platform was designed to be used as a smart Serial to Serial converter. It comes in a DC powered Din-Rail Mountable compact cabinet for ease of portability and installation. Standard protocols such as Modicon Modbus and Allen Bradley’s DF1 exist already. Other protocols and operations are easily programmed per customer’s requests.

The DL4000 has three serial channels, CHA, CHB, and CHC for intermixing protocols and communication standards. RS232C, RS422 and RS485 are available on CHA and CHB, while CHC only does RS232. Configuration of the operating parameters is done quickly and easily by the DL32 V3.X for all DL4000 models except DL4000-DMX use EQ32, both EQ32 and DL32 are windows based software shipped with the unit or available on the Equustek Website. Currently there are five standard DL4000 products available and many other customized ASCII protocol interfaces have been done.

Contact Equustek Solutions to see if the DL4000 is the correct device for your communication needs.

The DL4000-DMX is a two port device that bridges your Modicon Modbus devices to ones using the DF1 protocol. The DMX can either be used as Modbus Master or Slave as well as having both Modbus ASCII and RTU protocols.

The DL4000-DFX is a three port DF1 device. This will allow Two DF1 devices to talk to one CH0 of a PLC or SLC. The ability to intermix Half-Duplex and Full Duplex, or RS232 and RS422 greatly improves the effectiveness of the PLC’s CH0 programming port

The DL4000-MMX allows Modbus RTU devices to communicate with multiple Modbus ASCII devices. The DL4000-DAS interfaces Serial ASCII devices (Scanners/Printers) to A-B’s DF1 protocol.

The DL4000-MAS interfaces Serial ASCII Scanners to Modicon’s Modbus Protocol. The DL4000-MAS acts as a Modbus Master device and writes the ASCII data to a specific register in a specified slave device.

Using Wonderware’s ABTCP driver with the EQ7000

Wonderware’s ABTCP IO Server is capable of reading and writing data to devices on the DH+ using the EQ7000. Before any data can be read or written, a new local host must be created in the host file and a topic must be defined in the ABTCP IO Server.

Configuring the Hosts File The hosts file contains the names of local hosts and the IP addresses that are assigned to them. You must add a new entry to the hosts file with the IP address of the EQ7000. Below are the steps to adding a new entry to the hosts file.

1. Locate and open the hosts file. The host file can be found in the following directory. C:\WINDOWS\system32\drivers\etc

2. Open the hosts file using a text editor like Notepad. You will see the following.











3. Add a line at the end of the file specifying a new host name and IP address and then save the file. In the example below, the host name EQ7000 is added and has an IP address of









Click for more info




Communicating via Allen Bradley Ethernet ip protocol


The EQ7000 can accept messages sent by the Allen Bradley ethernet ip protocol. Therefore devices capable of communicating using Allen Bradley ethernet protocol can access devices on the DH+ network. Browsing specific nodes on the DH+ network is possible using RSLinx.


To do this, an Ethernet driver must be configured in RSLinx gateway with the IP address of the EQ7000 mapped to each node that exists on the network. Sending Messages to DH+ devices To communicate to nodes on the DH+ network using AB Ethernet switch, remote messaging must be used. Using local messaging will only allow communication to a single device located at node 0 on the DH+. When using remote messaging, the source and destination link ID’s are not needed and can be left as 0. The destination address (or remote address) will be the value of the DH+ node address. Please note that DH+ uses octal notation and the application that is being used to setup the message may use decimal notation.Below is an example of how to setup a remote message in a SLC 5/05 to read data from node 7 on the DH+ network through the EQ7000 at





Ethernet/ip to dh+

Equustek produces Ethernet/ip to dh+ protocol converters and network gateways

Lots of people are asking the question, “why go with the Ethernet/IP gateway to DH+ instead of updating all my Allen Bradley Equipment such as PLC5s to Ethernet/ip ?”

There is an excellent answer to this, The Ethernet/IP gateway to DH+ has supplied a solution to many of our problems, it has created existence a hell of a lot simpler for (A-B) Allen Bradley PLC(programmable logic controller) consumers as it has enabled them to never want the possibility to upgrade all their Allen Bradley software and equipment. Imagine never needing to upgrade the equipment again, no more spending cash every time time an update occurs, Thanks to Ethernet/IP gateway to DH +, you need to fork this money out, as you’ll be taken good care of for good.

The total cost of the ethernet/ip dh+ is also cheap, you can actually save your self a good amount of cash. If you use ethernet/ip dh+ converters, you do not have to upgrade each PLC with an Ethernet processor . The Ethernet/IP gateway is as easy as things can get. What you have to realize is the fact that you will never have to to update each PLC with an Ethernet processor.

Industrial Ethernet Systems

Industrial Ethernet Gateways

Ethernet TCP/ip address timing’s unknown nature has for ages been a downside for most professional system programs, especially people that have realtime ability demands that are strict. However, as the total price vs. gain efficiency has enhanced over time, commercial consumers are suffering from strategies to beat the evident short-comings.


As a whole, there are now about thirty commercial Ethernet techniques in use all over the world, but these most critical to the us marketplace are:

  • Ethernet/IP
  • Modbus/TCP
  • EtherCAT®
  • Ethernet Powerlink
  • Profinet

Every one of these methods have already been developed together with the problems of realtime handle in head (routine times, low-latency, low that was steady) the plan of preventive steps to prevent data collisions, plus the option was contacted by them in manners that were various.

The one noticeable distinction to the regular TCP/internet protocol address method is the enactment of real-time Info trade segments that are further on the top or that manage real time communication-either in location.

However, all methods carry on assistance for the Ethernet (IEEE 802.3) real and data layers and TCP/ip address/UDP, therefore supplying an interface to normal advice stage sites.

Methods like Modbus and Ethernet/IP /TCP seem to function as the most vulnerable in terms of realtime management that is difficult, since they inherited most of the characteristics that leave Ethernet TCP/ ip address low -deterministic. While the CSMA/CD dilemma ( arbitrary delay instances after coach settlement ) may be somewhat suppressed through the application of Ethernet changes, these practices nevertheless have to cope with the further jitter brought on by UDP and ip address. Without careful layout thoughts, they are going to not be unquestionable for motion control applications that are speedy, especially for challenging real time management.


Ethernet Powerlink circumvents the CSMA problem quite stylishly through circumventing the TCP/ip address/UDP levels as it pertains to communicating that is real time. Exceptionally deterministic and committed time-slices put to every node in the community are utilized by Ethernet Powerlink. The effect is while other nodes wait for his or her change, the fact that just one node carries data to the coach all through its time cut that is committed. This process therefore removes arbitrary and efficiently prevents any information crash dwell times. Clearly, the ip address jitter is additionally eliminated by the circumventing of TCP/IP/UDP.


EtherCAT nevertheless, approached by removing it totally in the real level, which, in most effect, demands the application of a dedicated equipment the CD difficulty. While an (registered company) grasp method needs merely a standard Ethernet network software, each (registered company) device takes a control that is committed. EtherCAT(registered company) nevertheless uses Ethernet as the physical level, Nevertheless, the Ethernet communications are passed from node to (daisychain), so getting rid of the requirement for bus settlement per CSMA/c d.


Profinet, when compared with any or all other practices released here, has experienced a transition through all previously detailed situations: Profinet V-1 (CBA) uses the common Ethernet TCP/IP, Profinet V-2 (RT) circumvents the TCP/ip address/UDP levels, while Profinet V3 (IRT) utilises a dedicated Ethernet control.






Serial to Ethernet Converter

What is a serial to ethernet converter?

A serial to Ethernet converter is a small electronic device which can transform Ethernet ip address/TCP packages to either RS232, RS485 or RS422 serial data signs and vice versa. Additionally it is occasionally called a sequential device machine and it comes in various sizes and shapes.

A serial Ethernet converter may have one serial interface or it can have several sequential ports, to 25 interfaces or even more.

Some Ethernet converters just has an RS-232 interface and a number of has an RS485 software and an RS232, among others the others H-AS all 3 interfaces (RS-232, RS485 and RS-422) constructed in.

Most typically it can be used for linking a serial RS-232, RS485 or RS-422 apparatus such as a commercial device into a pc over a typical LAN system, with a serial interface. The best thing about this is clear;You don’t have to wander all-the-way to the industrial plant to test your serial device’s other end.

How can a serial Ethernet converter function?

The circuitry within the convertor may change TCP/IP  packets to also change the information that is sequential to ip address and serial data packets, so that it operates in both ways.

The IP number of the Ethernet converter that was serial it self may even be altered to your own configuration settings.

Data Highway Plus -Dh+

Data Highway plus-Dh+

This is a networking protocol package for automation. It’s common practice in technology to convey protocols in levels of functions. The information Highway Plus package comprises three levels. All these will be the application-layer, the datalink layer as well as the actual level.

The hardware used within the Data Highway Plus community, particularly the cable is specified by the Data Highway Plus real layer. The information Highway Plus community is organized as a “bus.” The bus topology is one wire to which many nodes are linked. The cable specified for this network is baseband shielded twin axial cable.

Data Highway Plus utilizes a token-passing method called “floating master.”

The holder doesn’t have to test in the event the cable can be obtained because possession provides handle of the cable and is the grasp on the community. A node waits before the token is received, if it needs to carry to a different node. If the token is received by it, but doesn’t want to carry any data, it passes the token onto another node.
The transmitter waits for a response in the receiver before sending the following section when data is sent. This reply comes in the shape of an “ACK” (which means “got it”) or a “NAK” (which means “I cannot consider it”). A message which is responded to by a NAK will not be resent. If the initial transmission will not receive an ACK or a NAK inside a predetermined period, the message is resent. A message could be sent a maximum of three-times.


The Data Highway Plus method specifies a small pair of message types. These communications have a header with all the message type title within it. The message may carry application data, or might either be handle messages. Communications are ASCII (American Standard Code for Information Interchange) control requirements — all these are non-printable characters symbolized by a number in the table (they tend not to represent numbers).

The Data Highway Plus protocol’s purpose is to take instructions to your PLC (programmable logic control) that regulates a piece of commercial machinery. The process specifies a note box format to take these instructions. The message header contains a byte each to clarify the origin of the message, the destination of the command and also the message to be ran. There is also, additionally, a byte. The answer to this command will reply in a package headed by control, destination and source bytes, followed by a couple of bytes for status requirements. Commands and answers are matched together with a TNS (“trade”) code. The answer to a control will comprise the TNS of the order to which it’s an answer. Both the order message as well as the answer information can additionally have an info area.




Modbus RTU is an open (RS232 or RS 485) protocol derived from the Master/Slave architecture. This is a widely recognized protocol because of its ease of use and reliability. This broad acceptance is due in large part to MODBUS RTU’s simple use.

MODBUS RTU messages really are a simple 16-bit CRC (Cyclic- Checksum). The simplicity of these messages is always to ensure dependability. As a result of this ease, the basic 16-bit MODBUS RTU register construction may be used to pack in ASCII text, tables, floating-point, queues, along with other unrelated data.

MODBUS is considered an application layer messaging protocol, providing Master/Slave communicating between devices linked through buses or networks. At level 7, MODBUS is positioned on the OSI model. MODBUS protocol is supposed to be a request/response protocol and offers services specified by function codes. The function codes of MODBUS are elements of MODBUS’ request/answer PDUs (Protocol Data Unit)

A MODBUS transaction must be initiated by the customer, so that you can build the MODBUS program data unit. It is the function which informs the host about which form of activity to perform. The MODBUS program protocol establishs a petition initiated by way of a Master’s format. Only codes within the number of 1 through 255 are considered valid, with 128-255 being earmarked for exception answers. It’s the function code area which advises the server of what sort of action to perform when a note is sent by the Master to the Slave.

To define multiple activities, some functions may have sub- function codes added to them. For example, the Master is able to read the ON/OFF states of a group of inputs or discreet outputs.  When the Master gets the Slave response, the Slave uss the function code field to signal either a mistake- an exception answer or free response. The Slave repeats to the petition of the primary function code in the event of a normal response.

Data Item Properties
MODBUS RTU converter packets are merely intended to send information; they do not have the potential to send parameters like point name, resolution, components, etc. In the event the power to send such parameters is needed, you ought to inquire alternative protocols that are modern, EtherNet/IP, or a BACnet.

MODBUS RTU versus Other Protocols

Despite the restrictions of MODBUS RTU, there are nonetheless several good reasons as to the reason why it is still a challenger among industrial automation protocols. For one, MODBUS RTU is a dominating force in the market place and is a lot easier to execute than newer protocols. MODBUS RTU also requires considerably less memory. To implement MODBUS RTU, it is possible to fit the necessary size of 2Kb on a small 8- bit CPU or PIC processor, whereas with BACnet and EtherNet /ip address, you could possibly require 30-100Kb of memory.

Standard MODBUS RTU node addresses are 1-254, with 0 write just and being reserved for broadcast messages. Yet the 0 address is rarely used because of the fact there is no evidence the message was properly received in the slave node. This doesn’t have much influence if your physical layer is RS-232 as just one node can be implemented anyway. RS-485 while some some drivers will allow you to extend the sum of money limits the amount of nodes to 32.


The simplest difference between MODBUS RTU and MODBUS TCP communication protocols (also called MODBUS IP, MODBUS EtherNet, and MODBUS TCP/ip address) is that MODBUS TCP runs on an Ethernet physical layer and Modbus RTU is a serial level protoCol. Modbus TCP also uses a-6 byte header allowing routing.

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