Ethernet/IP Protocol

Read Wait Timeout

Waiting between individual reads of data from the communication if no data has been received..

Batch Size

The number of messages after sending of which, the Send Delay is performed.

Send Delay

Waiting after sending a batch consisting of Batch Size message. The purpose is not to overload the device with too many messages.
Note: while testing the Micro820 device, problems were encountered when sending approximately 200 messages  (browsing instances of the class File Object [0x37] with zero delay. Waiting for 1 ms solved the problem.

Max Pending Requests

Maximum number of unacknowledged messages. If the number of unacknowledged messages reaches the value of the parameter, the KOM process waits before sending the next message. A value of 1 means that each message must be confirmed before sending another one (so that the PLC cannot be overloaded due to intensive communication).

Write Symbolic: Array Elements

Methods of writing an array using symbolic addressing (Rockwell). There are three supported modes:

• 0 .. Array Index + Item Count: all the elements defined for a particular point are written (Array Index+1 or Item Count, whichever is greater)

• 0 .. Array Index: minimalistic variant - elements from 0 to Array Index are written

• 0 .. Max Array Index: maximalist variant - entries from 0 to Max Array Index are written, where Max Array Index is the largest number of elements of all I/O tags with the same symbolic address (within the station)

Optimized write of array element

Optimized write is used when only one array element is written. Optimization consists of writing only one specific element and specifying its index (in the protocol specified as Member ID).
Note: the tested Micro820 device supported the optimization, the test software server did not.

Max Packet Size

The maximum size of Ethernet/IP messages (Unconnected Explicit message) - according to the standard 504 bytes.
Note: in symbolic mode (Rockwell) it is also possible to work with larger arrays using proprietary services Read Tag Fragmented Service and Write Tag Fragmented Service.
Note: this size does not include the Encapsulation Header (24 bytes - Command/Length/Session Handle/Status/Sender Context/Options) or the SendRRData/Common Packet Format header (16 bytes - Interface Handle/Timeout/Item1 + Length/Item2 Length).
Note: values ​​greater than 504 bytes are used only if the parameters Use Connected Transport and Large Forward Open have the value YES (Connected Explicit Messages are used and the CIP connection is established with the Large Forward Open message).
Note: for a specific CompactLogix (1769-L24ER-QBFC1B/A LOGIX5324ER) the maximum value of the parameter was 4002. For larger values, the response to the Large Forward Open message contained an error code:
Received Rockwell LargeForwardOpen Response [xDB] with GeneralStatus: Connection failure [x01], Additional status: <09><01><A2><0F> INVALID CONNECTION SIZE

Response Timeout

Timeout to receive an answer for a request. If the response for a request is not received within this time, this is considered an error, and the TCP connection will be closed.

Optimized Work with Symbolic Names

Optimization of work in a symbolic mode (Rockwell) - so-called Symbol Instance Addressing. Instead of using symbolic names, a Symbol Instance ID is used for reading. The Symbolic name is converted to the Instance identifier by the same service which is used for browsing.
Note: Not every device or Rockwell firmware version supports this optimization (tested Micro820 with firmware 10.0.12 or 11.0.11 did not support this optimization). In this case, if the device returns the Service not supported [0x08] error code, the optimization will be disabled until the KOM process is restarted or the configuration of the respective line is re-saved.

TCP No Delay

Setting the TCP No Delay parameter to YES causes the low-level socket option TCP_NODELAY to be set, thus turning off the default packet coalesce feature.

An octet string representing the parameter Route_Path (of padded EPATH type, that is, the number of octets in each segment must be even). If this parameter is specified, the protocol messages (Get_Attribute_Single, Set_Attribute_Single, Read Tag [Fragmented] Service, Write Tag [Fragmented] Service) will be wrapped in an Unconnected Send message that is used for routing.

It was not necessary to set this parameter when communicating with Micro820, MicroLogix 1100, and CompactLogix devices.

When communicating with ControlLogix via the ControlLogix EtherNet/IP bridge Module (1756-EN2TR/C), it was necessary to set the parameter to 01 00, which according to protocol documentation means Port 1 (which represents the backplane) and slot 0 (where the Central Processor was located). 

To communicate with the processor in slot 1, the parameter had to be set to 01 01, so the general syntax for accessing a slot XX would be 01 XX.

A more complicated configuration consisting of 3 segments:

• we go through the processor in slot 0: 01 (Backplane) 00 (Slot 0)

• then we go through port 2 to the IP address 172.25.58.11: 12 (port 2 with the Extended flag in the 5th bit, which means a 1-byte length follows) 0C (data length=12 bytes) 31 37 32 2E 32 35 2E 35 38 2E 31 31 (ASCII codes of IP address 172.25.58.11).
  Note: If the number of characters in the string was odd (e.g. 13), then the length (e.g. 0D) would be followed by an IP address (13 bytes) and then a padding octet 00 to make the number of octets of this segment of the path even.

• and finally, we go to the processor in slot 1: 01 (Backplane) 01 (Slot 1)

so the whole Route Path string is: 01 00 12 0C 31 37 32 2E 32 35 2E 35 38 2E 31 31 01 01 (in the syntax of Rockwell OPC server it is "1,[0,2,172.25.58.11, 1], 1")

octet string

Setting the parameter to YES causes the protocol messages Read Tag Service to be wrapped in a Multiple Service Packet Service message. This parameter is used for communication optimization (wrapping several messages into one), while the size of one message (Unconnected Explicit message) does not exceed the Max Packet Size value.
Note: This feature is not supported on older PLCs (e.g., SLC 5/05 and PLC5E).
Note: On a specific CompactLogix 1769-L36ERM, the parameter setting accelerated the reading cycle of 1000 objects from 15 seconds to 2.2 seconds.

YES/NO

NO

Optimized structure reading can be used to read the entire structure from the PLC at once instead of reading individual members. Each structure has a defined template in the PLC (UDT- user data template). Optimized reading requires finding the structure (a list of individual elements, their types, and offsets within the structure).
Reading the list can take several tens of seconds, so after successful reading, it is saved in the file Cache-<Link_name>-<RoutePath>.txt in the Cache subdirectory in the application directory. When starting communication, information about structures and templates is read from the cache as a priority.
Example of cache file name: Cache-L.CS.CSVV-0100.txt for line L.CS.CSVV and parameter value Route Path=01 00.

In the configuration of I/O tags, it is necessary to create one I/O tag with the structure address (e.g. Struct1) with Reading mode = Active read (this I/O tag will still be invalid, but will be used to generate read requests) and the other I/O tags with the addresses of the structure members (e.g. Struct1.MyValA, Struct1.MyValB) with Reading mode = Passive read.

Note: In the case of large structures containing substructures, it is up to the application programmer to configure either an I/O tag for reading the entire structure (e.g. Struct2) or multiple I/O tags for reading substructures (e.g. Struct2.SubA and Struct2.SubB) - and find out what is optimal in a specific case in terms of speed and PLC load.

Note: If the structure contains internal data structures (e.g. TIMER, COUNTER, CONTROL, MESSAGE, MOTION members) to which symbolic access is not allowed, reading the entire structure will fail (error "Privilege violation [x0F]", with "Additional status" set to "Reserved by CIP").

Note: Deleting the cache file from disk and saving the communication station will cause the list of structures and templates to be reloaded and the cache file to be recreated. This may take several tens of seconds, depending on the number of structures and UDTs.

YES/NO

NO

When Optimized Structure Read was active, in specific cases, it happened that a large template definition was not received in its entirety, but the name of the last member was truncated (e.g., missing 2 characters and a terminating 0). This happened when the message definition did not fit into one packet, but was larger (e.g., it should have been 861 or 2225 bytes). Setting this parameter to 2 or 3 (and requesting the corresponding number of bytes more) solved the problem.

Problematic device parameters:

• ControlLogix: 1756-L55/A 1756-M23/A LOGIX5555, Module Revision: 15.004

• Communication card 1756-ENBT/A, Product Revision: 3.009 Build 1, Firmware Version Date: Oct 11 2005, 08:27:13

• ControlLogix: 1756-L61/B LOGIX5561, Module Revision: 17.003
  Communication card 1756-ENBT/A, Product Revision: 3.009 Build 1, Firmware Version Date: Oct 11 2005, 08:27:13

0-23

0

The parameter enables the use of connected CIP transport. Instead of Unconnected Send, a connection is created (with a Forward Open/Large Forward Open message) and then messages are sent through the created connection.

YES/NO

NO

The number of parallel logical CIP connections. A larger number allows faster handling of messages, on the other hand, PLCs support a limited number of CIP connections. Only one message can be handled by one CIP connection at a time.
See the document EtherNet/IP Network Devices, table on page 22.

1-16

4

The parameter specifies the ID of the first logical CIP connection. If CIP Connections>1, then the configured and subsequent IDs (e.g. 10, 11, 12) are used. IDs of logical CIP connections must be unique, i.e. if there are several stations (on one/multiple lines) that communicate with the same PLC using connected CIP transport (Use Connected Transport=YES), it is necessary to configure a non-repeating ID.

0-65535

1

The Connection Path parameter of the Forward Open/Large Forward Open message. The default value means:

• 01 - Port segment: Backplane

• 00 - Link Address: 0

• 20 - Path Segment: 0x20 (8-Bit Class Segment)

• 02 - Class: Message Router (0x02)

• 24 - Path Segment: 0x24 (8-Bit Instance Segment)

• 01 - Instance: 0x01

octet string

01 00 20 02 24 01

The Vendor ID parameter of the Forward Open/Large Forward Open message indicates the vendor ID (identification of the D2000 KOM process).

0 - 65535

0x1234

The Tick Time parameter of the Forward Open/Large Forward Open message indicates the size of the time interval used to calculate the Forward Open message timeout. See the Timeout Ticks parameter.

ms

128

The Timeout Ticks parameter specifies the number of time intervals (of size Tick Time) used to calculate the Forward Open/Large Forward Open message timeout. Timeout is calculated as Tick Time * Timeout Ticks.

-

1-255

The O->T RPI parameter of the Forward Open/Large Forward Open message indicates the size of the Originator -> Target Requested Packet Interval in microseconds.
Definition from the Common Industrial Protocol standard: The requested packet interval shall be the time between packets requested by the receiving device. The value shall be used to allocate bandwidth at each of the producing nodes. The allocation of bandwidth may have to be adjusted when the actual packet rate or actual packet interval is returned, since it is possible for the two values to differ.

 μs

2000000

The T->O RPI parameter of the Forward Open/Large Forward Open message indicates the size of the Target -> Originator Requested Packet Interval in microseconds.

 μs

2000000

Parameter Connection Timeout Multiplier of Forward Open/Large Forward Open messages. Specifies the multiplier by which the O->T RPI and T->O RPI parameters are multiplied to determine the timeout of the CIP connection in the O->T or T->O direction.
The default timeout is therefore 2 000 000 μs * 16 = 32 seconds.
Note: the parameters Connection Timeout Multiplier, O->T RPI and T->O RPI must be adjusted if the period/reading values ​​defined on the station is greater than the CIP timeout because the CIP connection may expire during inactivity.

x2 - x512

x16

The parameter allows a Large Forward Open message to be used instead of a Forward Open message to create a connected CIP transport. In this, it is also possible to specify a larger size of the Connection Size parameter than 504 bytes, so that the messages can be larger. See the note on the Max Packet Size parameter which specifies the Connection Size for Forward Open/Large Forward Open.

YES/NO

NO

Setting the parameter to a non-zero value causes the use of the PCCC protocol encapsulated in the Ethernet/IP protocol. In this way, it is possible to communicate with older SLC 5/05 and PLC5E. At the same time, the symbolic address of the I/O tag starts to be interpreted as an address in SLC-500 format - see Allen-Bradley CSP/PCCC protocol (e.g. N:3 or $T4:0/ACC).
Note: after changing the parameter from 0 to a non-zero value or back, it is necessary to re-save the I/O tags, restart the KOM process or use the RELOAD command.

0-240 bytes

0

Selection of PCCC commands used for communication with older SLC 5/05 and PLC5E if the PCCC Max Data Length parameter is set to a non-zero value. The following options are available for selection:

• Typed Read (68), PLC5 logical ASCII addressing (*)

• Typed Read (68), PLC5 logical binary addressing (*)

• SLC Protected Typed Logical Read (A1/A2)

* - when using these commands, only writing is supported for the file types Status (S), Binary (B), Integer (N), Float (F), and even for these types only writing of whole elements is supported, not bits. Writing is not supported for the Timer (T) and Counter (C) file types. 

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