Omron SYSMAC CJ1W-PRM21, Operation Manual

Page: 165 / 190

151
Appendix B
Slave Diagnostics Message
B-1 Slave Diagnostics Data Message
Every PROFIBUS-DP slave device has to support the transfer of a-cyclic diagnostics message. The contents
of these messages allow a PROFIBUS-DP Master Unit to assess the status of the slave device in every state of
the communication. The diagnostics message format is defined in the PROFIBUS standard.
The slave diagnostics message consists of at least 6 mandatory bytes. If supported, the slave can send addi-
tional extended diagnostics bytes in the same message. The extended diagnostics format is defined in the
PROFIBUS standard. The extended bytes are usually only included in the diagnostics message if an event has
occurred, which results in extended diagnostics.
In some cases the PROFIBUS-DP Master unit will itself form a slave Diagnostics message. This is the case if
the slave station is not responding to any request sent by the Master Unit. The format of the message will be
the same as a message sent by a slave station, but the contents has been sent by the Master Unit.
The last received diagnostics message for each slave station allocated to the PROFIBUS-DP Master Unit can
at any time be retrieved from the Unit though the MEMORY AREA READ FINS command.
B-2 MEMORY AREA READ (0101)
In order to retrieve the last received slave diagnostics message from the PROFIBUS-DP Master unit, the PLC
CMND(490) can be used to transmit a MEMORY AREA READ FINS command to the PROFIBUS-DP Master
unit. The MEMORY AREA READ command format is given below.
Command Format
Response format
Parameters
• Data specifier code (command)
Defines the data to be retrieved from the Unit. Always set to 81 FF 00 (Hex).
• Slave station address (command)
Defines the slave station network address. Set to 00 ~ 7D (Hex).
• Number of items to read (command)
Defines the number of bytes to read. Set to 1 ~ F4 (Hex).
The diagnostics message is returned from the slave device as a sequence of bytes. When transferred to the
PLC memory, the format is converted to words. The format is shown in the figure below. The location in the
PLC memory, designated as D is the Destination location as specified in the CMND (490) instruction.
Slave station address
No. of items
(binary)
Command
code
01 01
Data specifier
FF 81 00
End code Command
code
01 01
Diagnostics data
(for number of items)