Slave Diagnostics Message - Omron SYSMAC CS Series Operation Manual

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 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 Master Unit will itself form a slave Diagnostics message. This is the case if the
slave device 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 device, but the contents has been sent by the Master Unit.
The last received diagnostics message for each slave device allocated to the PROFIBUS Master Unit can at
any time be retrieved from the Unit through 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 Master Unit, the PLC
CMND(490) can be used to transmit a MEMORY AREA READ FINS command to the PROFIBUS 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 device address (command)
Defines the slave device 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.
Appendix B

Slave Diagnostics Message

01 01 81 FF 00
Command
Data specifier
code
Slave station address
01 01
Command End code
code
No. of items
(binary)
Diagnostics data
(for number of items)
233