4

Communications Status Words

The COMMREQ Status word (CRS word) reports status in the format shown below. The CRS word location is specified in Words 3 and 4 of the Command Block.

CRS Word in

Hex Format

High Low

00 00

Minor Error Codes (high byte)

Success and Major Error Codes (low byte)

There are several points to remember when interpreting the contents of the COMMREQ Status word:

1.Display the Status Words in hexadecimal form to more easily differentiate the high and low bytes. A good way to do this is to use a MOVE WORD function block to display the hexadecimal value within the ladder program.

2.The Ethernet Interface will never send a zero for the COMMREQ Status word to the PLC CPU. The user program should zero the COMMREQ Status word before issuing the COMMREQ function and then check for a non-zero value indicating that the Ethernet Interface is responding to the COMMREQ. A good way to do this is to use a MOVE WORD function block to zero the CRS word.

3.A status code of 1 in the low byte and 0 in the high byte indicates that the request was successful. All other non-zero values indicate errors. Refer to the tables below for a complete listing of major and minor error codes.

Major Error Codes

The following tables list the error codes that are reported in the COMMREQ Status word after the execution of a COMMREQ function.

Error Status

Major Error Description

Hexadecimal

 

 

 

01H

Successful Completion.

 

 

87H

The client PLC CPU’s Service Request Queue is full.

 

 

8BH

Illegal Service Request. The requested service is either not defined or

 

not supported. (This value is returned in lieu of the actual service

 

request error (01H), to avoid confusion with the normal successful

 

COMMREQ completion.

 

 

90H

Client API Error. See the following table of Minor Error codes.

 

 

91H

Modbus/TCP Error Codes at server. An error was detected at the

 

Modbus/TCP server. See the following table for the Minor Error codes.

 

 

GFK-1541B

Chapter 4 Programming Modbus/TCP Channel Commands

4-23

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GE GFK-1541B manual 8BH