Instruction manual

Connection box C-BOX 300
The C-BOX PROFIBUS protocol implementation
S
ubject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany
Pepperl+Fuchs Group • Tel.: Germany (06 21) 7 76-0 • USA (330) 4 25 35 55 • Singapore 7 79 90 91 • Internet http://www.pepperl-fuchs.com
Date od issue 07/25/2003
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Figure 5.2 Data frame structure
5.5 Control field
The Input field structure reserves IN[0] for handshake purposes: bit 0 and bit 1 are
used for this. Bit 6 and 7 are set to 0 in order to specify the messaging protocol
number 0 is in use. They cannot be used for other purposes.
The Output field structure is symmetrical, and reserves bit 0 and 1 for handshake
purposes. Bit 6 and 7 are set to 0 to indicate the messaging protocol number 0 is in
use.
Bit 2 of the Output buffer is used to request a clear of the synchronization numbers
(bit 0 and bit 1 of both Input and Output buffers). This is called a resynchronization
request and it is always initiated by the Master Station. The Slave must acknowledge
the request, using bit 2 of the Input buffer.
Bit 3 is used to control a fragmentation sequence in both directions.
• byte 2: Service Access Point Field, used to distinguish among different ser-
vices but also to provide future expandability. Since this SAP definition
is introduced by the Datalogic PROFIBUS Driver, it must not be con-
fused with the PROFIBUS SAP that is defined by the international
standard.
• byte 3: Length Field, that contains the number of bytes used by the application
layer. This number must always be less than or equal to MaxInBytes-4
for the IN[] buffer and less than or equal to MaxOutBytes-4 for the
OUT[] buffer.
Application Data Buffer [Length Bytes]
Exchange Area Buffer [Max (IN/OUT Bytes]
byte 3 = Length Field
byte 2 = SAP Field
byte 1 = Profibus Station Address Field
byte 0 = Control Field
0 1 2 3 ... ...