GE GFK-0804B Communication Errors

C
C-18 Micro PLC Programmer’s Guide – April 1994 GFK-0804B
Communication Errors
Communication errors are divided into three groups:
Invalid Query Message
Serial Link Time Outs
Invalid 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
Invalid Address Field 2
Invalid Data Field 3
Query Processing Failure 4
The format for an error response to a query is as follows:
Address Check
ErrorException
Func Error Subcode
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 numbe r 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).