GE GFK-0804B Communication Errors, Invalid Query Message, Invalid Function Code Error Response

C

Communication Errors

Communication errors are divided into three groups:

HInvalid Query Message

HSerial Link Time Outs

HInvalid Transaction

Invalid Query Message

When the Micro PLC receives a query addressed to itself, but cannot process the query, it sends one of the following error responses:

	Subcode
Invalid Function Code	1
InvalidAddress Field	2
Invalid Data Field	3
Query Processing Failure	4

The format for an error response to a query is as follows:

Address Exception Func

Error

Subcode

Error Check

The address reflects the address provided on the original request. The exception func- tion code is equal to the sum of the function code of the query plus 128. The error sub- code is equal to 1, 2, 3, or 4. The value of the subcode indicates the reason the query could not be processed.

Invalid Function Code Error Response (1)

An error response with a subcode of 1 is called an invalid function code error response. This response is sent by the Micro PLC if it receives a query whose function code is not equal to 1 through 8, 15, 16, or 17.

Invalid Address Error Response (2)

An error response with a subcode of 2 is called an invalid address error response. This error response is sent in the following cases:

1.The starting point number and number of points fields specify output points or input points that are not available in the Micro PLC (returned for function codes 1, 2, 15).

2.The starting register number and number of registers fields specify registers that are not available in the Micro PLC (returned for function codes 3, 4, 16).

3.The starting analog input number and analog input number fields specify analog inputs that are not available in the Micro PLC (returned for function code 4).

4.The point number field specifies an output point not available in the Micro PLC (returned for function code 5).

C-18 Micro PLC Programmer's Guide ± April 1994 GFK-0804B