Slave Diagnostics Message; A-7-1 Slave Diagnostics Data Message - Omron CJ Series Operation Manual

Appendices
A-7

Slave Diagnostics Message

A-7-1 Slave Diagnostics Data Message
Every PROFIBUS DP slave device has to support the transfer of acyclic 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 stan-
dard.
The slave diagnostics message consists of at least 6 mandatory bytes. If supported, the slave can send
additional 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 command (see 6-3-3
MEMORY AREA READ (0101)).
The diagnostics message is returned from the slave device as a sequence of bytes. When transferred
to the CPU memory, the format is converted to words. The format is shown in the figure below. The
location in the CPU memory, designated as D is the Destination location as specified in the MEMORY
AREA READ command.
The first 6 bytes or 3 words (Word D to Word D+2) are mandatory bytes, which will always be sent by
the slave device. Any additional, i.e. extended diagnostics bytes start at Word D+3. The contents of the
first six bytes is defined by the PROFIBUS standard. The contents of the extended diagnostics informa-
tion is slave device dependent, but the format is defined in the PROFIBUS standard.
The first 6 bytes and the Extended diagnostics format are explained below.
A-24
D Byte 1 Byte 2
D + 1 Byte 3 Byte 4
D + 2 Byte 5 Byte 6
D + 3 Byte 7 Byte 8
D + 4 Byte 9 Byte 10
CJ-series PROFIBUS Master Unit Operation Manual for NJ-series CPU Unit (W509)