Datalogic GWY-01-PBS-01, Reference Manual

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PROFIBUS INTERFACE
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5
5.4 PROTOCOL IMPLEMENTATION
5.4.1 Definitions
In the protocol description we'll use the following definitions:

Input field: is the set of master inputs that can be modified by the specific slave

Output field: is the set of master outputs that can be read by the specific slave

MaxInBytes: is the number of input bytes shared by the master and the specific slave

MaxOutBytes: is the number of output bytes shared by the master and the specific
slave

IN[ Nin ] represent the input byte number Nin, where numbering starts from 0 to
MaxInBytes-1

OUT[ Nout ] represent the output byte number Nout, where numbering starts from 0
to MaxOutBytes-1
Obviously, MaxInBytes and MaxOutBytes are respectively the configured
INPUT and
OUTPUT AREA sizes.
The I/O Exchange Areas are actually updated and read every 30 ms at the Gateway Profibus
side. So after an RFID tag is read the worst delivery time from the Gateway Profibus to the
Master station is about 30 ms plus the intrinsic PROFIBUS DP delay and the Master delay.
This product implements the Datalogic AnyBus Driver (DAD) which is a layer that is built
upon the intrinsic fieldbus data exchange mechanism. The Driver is needed to add features
such as flow control and fragmentation.
In order to implement the flow controlled version of the driver, I/O Exchange Areas must be
congruently compiled in both directions.
INPUT Area is the Exchange buffer from Gateway
Profibus to the Master while OUTPUT Area is the exchange buffer from the Master to the
Gateway Profibus. Only the first three bytes are used by the Datalogic AnyBus Driver layer in
both buffers for the extended protocol.
These are:
byte 0: Control Field , used to issue and control the Datalogic AnyBus Driver
primitives such as flowcontrol, fragmentation and resynchronization;
byte 1: Service Access Point Field , used to distinguish among different services but
also to provide future expandibility. Since this SAP definition is introduced by the
Datalogic AnyBus Driver, it must not be confused with the AnyBus SAP that is defined
by the international standard.
byte 2: Length Field , that contains the number of bytes used by the application layer.
This number must always be less than or equal to MaxInBytes-3 for the IN[] buffer
and less than or equal to MaxOutBytes-3 for the OUT[] buffer.