Event-Oriented Data Exchange; Status Information In Event-Oriented Data Channel - Bosch Rexroth ID 40 Manual

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7.3 Event-oriented data exchange

With event-oriented data exchange, the data read by the unbuffered prefetch
(Chapter 6.4.1.1 "Unbuffered prefetch") is transmitted from the SLK to the fieldbus
master. Write access to the SLK is not possible in event-oriented data exchange.
All data in this channel is updated simultaneously once it has been read from the
data carrier.
The size of the event-oriented data channel is determined by I/O modules in
the Profibus GSD file, see Chapter 7.8 "Profibus GSD file". These modules are
designated by "... event-oriented data access".
Example:
Module "32 | event-oriented data access" reserves 32 bytes of input for event-
oriented data exchange in the cyclical data communication for Profibus.
Determining the I/O module for the event-oriented data channel is based on the
desired number of bytes that should be read by the system using the unbuffered
prefetch. Two status bytes containing important operational information (see below)
are added to this number.
Even if no unbuffered prefetch data is desired, at least two bytes have to be
reserved for the event-oriented data channel, since the ID 40/SLK-PDP shows
important system information here.
7.3.1

Status information in event-oriented data channel

The first two bytes in the event-oriented data exchange are status bytes with the
following structure:
Table 14: Status byte 0 of event-oriented data exchange
Byte 0 (bits 0–7)
7 6
Event counter
Bits 0 to 3 comprise the result code. The result code is zero once a previously
parameterized prefetch is executed without error. An error code greater than zero
indicates when errors occurred during the prefetch (e.g., unexpected break in
communication between SLK and MDT).
The coding for the result code is the same as for command-oriented data exchange
(see Chapter 7.5 "Profibus error codes").
Bits 4 to 7 comprise the event counter. The counter runs cyclically from 0 to 15 and
is increased by 1 when the current PRECONNECTED link state is ended. This signals
to the control system that the data from the prefetch parameterization is updated.
At this point, the user program can import prefetch data. The counter also increases
when no prefetch is parameterized.
5 4 3 2 1 0
Result code