Network Read (RX) Instruction

Mnemonic (Keyboard Shortcut) = RX

Icon / Button =

Purpose

Perform Read requests to other P Series CPU by Reading the Tags of specified CPUs over the Ethernet, RS232 or RS485 Ports on the CPU.

Instruction Parameters

Parameter	Parameter Type	Requirements	Description
Enable	Ladder Input	Must Have	Edge-driven. If Automatic Polling is selected, the instruction becomes Level-driven. When Enable is ON, the instruction will operate every scan. When Enable is OFF, the instruction is not solved, and its outputs are not updated.
Ethernet Port	Selectable Option with Drop-down Selection	Must Select Ethernet Port or Serial Port	CPU External Ethernet Port that will send Read requests.
IP Address	Constant	Must Have when Ethernet Port Selected	IP Address of the CPU server that the Read Request will be sent to. Enabled when Ethernet Port is selected.
TCP Port Number	Constant	Must Have when Ethernet Port Selected	Default is 502 (number specified by Modbus TCP specification). Some devices will require a different value. Enabled when Ethernet Port is selected.
Serial Port	Selectable Option with Drop-down Selection	Must Select Ethernet Port or Serial Port	RS232 or RS485 CPU Port that will Perform Read Requests.
Slave Node Number	Constant	Must Have when Serial Port Selected	Enter the Slave Node Number of the CPUfrom which toRead. The Slave Node Number is found in the Hardware Configuration for the Port on the CPU.
Use Structure	Checkbox	Optional	Enables the use of Structure.
In Progress	Boolean Tag	Optional	Status Bit that specifies a Read Request is in progress inside of the CPU (sent from the instruction but not yet sent out the Ethernet Port). The Status Bit reflects the Status of the individual Read Request.
Complete	Boolean Tag	Optional	Status Bit that specifies a Read Request has been sent and a reply has been received, but it may not necessarily have been a good reply. The Status Bit reflects the Status of the individual Read Request.
Success	Boolean Tag	Optional	Status Bit that specifies a Read Request has been sent and a good reply has been received. The Status Bit reflects the Status of the individual Read Request.
Error	Boolean Tag	Optional	Status Bit that specifies a Read Request has been sent and a reply with an Error has been received from the Slave device within the specified Timeout period. Check the Exception Response String to see if it's an Error returned from the Slave device or check the Error Logs to see if it is an Internal Error. The Status Bit reflects the Status of the individual Read Request.
Timeout	Boolean Tag	Optional	Status Bit that specifies a Read Request has been sent but no reply was received within the specified Timeout value time.> Timeout value is set up in the External Ethernet Port and RS232/RS485 Serial Ports of the Hardware Configuration. The Status Bit reflects the Status of the individual Read Request.
Exception Response String	String	Optional	String that holds the exception response Error. View the Communication Error Codes section of the help file for detailed information on Error Codes and possible corrective actions.
Automatic Polling	Checkbox	Optional	The CPU will send out a request at the specified Poll Rate + Offset Time Value (msec).

Parameter	Parameter Type	Requirements	Description
Skip Execution if Buffer is Greater Than	Checkbox	Optional	Used with Automatic Polling, allows the user to back-off an instruction if the buffer is getting too full (for CPU ports only). Set by a percentage. See more details in the Communications topic.
Remote Project	Constant	Must Have	Allows the user to select the Project's Tagname Database of the CPU that the instruction is targeting. Use the Read button to view Remote Projects.
Non- Array	Selectable Option	Must Select Non-Array or Array	Allows user to specify non-sequential Tags that can be Read in Read Request. The number of Tags entered determines Request size.
Tags of This Project	Numerical Tag	Must Have when Non-Array is Selected	Allows the user to select the Tags of this Project/CPU that the data will be Read into. Enabled when Non-Array is selected.
Tags of Remote Project	Numerical Tag	Must Have when Non-Array is Selected	Allows the user to select the Tags in the target Project/CPU that the data will be Read from. Enabled when Non-Array is selected.
Array	Selectable Option	Must Select Non-Array or Array	Allows the user to select the starting Tag and sequential number of Tags that will be Read in the Read Request.
Array Tag of This Project	Numerical Tag	Must Have when Array is Selected	Allows the user to select an Array Tag of this Project/CPU that the data will be Read into. Enabled when Array is selected.
Array Tag of Remote Project	Numerical Tag		Allows the user to select an Array Tag in the target Project/CPU that the data will be Read from. Enabled when Array is selected.
Starting Index	Constant		Starting Index position within the specified Array. Enabled when Array is selected.
End Index	Constant		Ending Index position within the specified Array. Enabled when Array is selected.
String Tag of This Project	String Tag	Must Have when String is Selected	Allows the user to select a String Tag of this Project/CPU that the data will be Readinto. Enabled when String is selected.
String Tag of Remote Project	String Tag		Allows the user to select a String Tag in the target Project/CPU that the data will be Read from. Enabled when String is selected.
Number of Characters	Constant		Enter number of characters, max 128.

Note: Communications using this instruction are performed through the External Ethernet Port located on the CPU.
P1 Single Ethernet Port Upper (P3) or forward (P2) of the Dual Ethernet Ports RS232 Port CPU (RJ12 Port) RS485 Port (3-pin Terminal Block).
Uses Modbus based protocol exclusive to the P Series CPUs.

Note: For Automatic Polling, the instruction will execute at the selected Poll Rate + the Poll Rate Offset if used.

Note: Tag Values are updated immediately as each Ladder Rung is executed, top to bottom. However, Tag Values representing physical Outputs are only applied to the physical Output after the END statement of the last Task to be scanned is reached. Outputs in Remote Base Groups have additional limitations regarding Update Intervals.

Note: Auto polling minimum value is determined by the end device response time. If you are getting errors due to requesting data too frequently, the auto polling rate will need to be increased until error condition clears.

Instruction Configuration

When Network Read Instruction is selected the window shown below opens with defaults shown.

Parameter Configuration Table

Network Read

Instruction

(RX)

Notes

* This icon indicates to use 1D Array data types of the respective Data Type column.

Ethernet Port

Select if Ethernet Port is used.

IP Address

Enter an IP Address.

TCP Port Number

Enter TCP Port Number. Default is 502.

Serial Port

Select if Serial Port is used.

Slave Node Number

Enter a Slave Node Number. Default is 1.

Use Structure

Select if Structures are used.

In Progress

Select a Boolean Tag for In Progress.

Complete

Select a Boolean Tag for Complete.

Success

Select a Boolean Tag for Success.

Error

Select a Boolean Tag for Error.

Timeout

Select a Boolean Tag for Timeout.

Exception Response String

Select a String Tag for Response Errors.

Automatic Polling

Select and enter Polling Time and Offset Time (msec).

Skip Execution

Select and enter % Value.

Remote Project

Select desired Remote Project.

Non-Array

Select if Non-Array Mapping is desired.

Tags of This Project

Enter the desired Tagnames> to be Mapped for this Project.

Tags of Remote Project

Enter the desired Remote Project Tagnames to be Mapped.

Array

Select if Array Mapping is desired.

Array Tag of This Project *

Enter the desired Tagnames to be Mapped for this Project.

Array Tag of Remote Project *

Enter the desired Remote Project Tagnames to be Mapped.

Starting Index

Enter the Starting Point of Mapped Array.

Ending Index

Enter the Ending Point of Mapped Array.

String

Select if String Mapping is desired.

String Tag of this Project

Enter the desired Tagname to be Mapped for this Project.

String Tag of Remote Project

Enter the desired Remote Project Tagname to be Mapped.

Number of Characters

Enter the number of Characters to be read.

Timing Charts

Note: Another side effect of the queuing mechanism is that the instruction status bits may not be seen in the ladder. When an instruction has completed (Success, Exception Response, or Timeout), the CPU firmware will set the appropriate status bits. At the point that the CPU firmware pulls another message off the queue, it will reset the status bits of that instruction. The timing can work out in such a way that the status bits get set but the CPU firmware pulls off the instruction that contains those same status bits and resets them to start another iteration before the ladder code examines those bits.
Two things can be done to ensure reliable detection of status bits:
1. Do not use Automatic Poll and use interlocking logic to detect status completion of an instruction before enabling that instruction again. This is the most reliable method.
2. Ensure that the Automatic Poll time is long enough to prevent queueing of that same instruction.
See Communications Modbus Functionality help topic for more details.

Application Example

In the following example, the CPU Ethernet Port is performing a Network Read of two Tags from another CPU in the network.