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Response Codes Section 6-7
6-7-2 Network Relay Errors
A network relay error will occur whenever a command cannot reach the desti-
nation. These errors can occur for several reasons: 1) Data was not success-
fully passed between two Link Units, 2) Data was not passed successfully
between a Link Unit and another Unit, such as the PLC’s CPU Unit, or 3) The
destination of a gateway does not exist. In any case, the Unit that was not able
to transfer data will return a response indicating a network relay error.
Bit 7 of the first byte of the response code will be ON if a network relay error
has occurred. When this happens, two more bytes of data will follow the
response code to indicate the location of the error. This information, along
with the response code, should enable you to track the error.
Error network address: 00 to 7F (Hex) (0 to 127 in decimal)
Error node address: Controller Link: 01 to 3E (Hex) (1 to 62 in decimal)
Ethernet: 01 to 7E (Hex) (1 to 126 in decimal)
SYSMAC NET: 01 to 7E (Hex) (1 to 126 in decimal)
SYSMAC LINK: 01 to 3E (Hex) (1 to 62 in decimal)
Relay Errors A relay error indicates that the command did not reach the Unit to which it was
sent. There are several types of situation in which this can occur. Example 1
(below) shows a situation in which a relay error occurs when data cannot be
transferred from one Communications Unit to another in an interconnected
network. Example 2 shows a similar situation, except that the destination Unit
is something other than a Communications Unit. In Example 3, the relay error
occurs because either the specified destination node or the next relay node
does not exist.
In the three diagrams, the numbers indicate the following:
(1)The transmitted data fails to be received.
(2)The relay error and response code are returned to the command
source.
Bit
1: PLC Non-fatal Error Flag
1: PLC Fatal Error Flag
Error network address Error node address
First word
Second word
Third word
Command code
1: Relay Error Flag
7654321076543210
First byte Second byte
Main response code (MRES)
7654321076543210
7654321076543210
Sub response code (SRES)