Instruction manual

Connection box C-BOX 300

The C-BOX PROFIBUS protocol implementation

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

5 The C-BOX PROFIBUS protocol implementation

5.1 Definitions

In the following description we will 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 Exchange Areas are actually updated and read every 30 ms at the C-BOX side.

So when a barcode is generated the worst delivery time from C-BOX to the Master

station is about 30 ms plus the intrinsic DP PROFIBUS delay and the Master delay

(here we neglect the case in which the internal input queue was previously used, see

the paragraph DPD internal queues).

5.2 C-BOX's PROFIBUS functional modes

Using PROFIBUS protocol Flow Control, four bytes of the PROFIBUS DP exchange

areas are reserved for driver operation. So the information field must begin at the fifth

byte. These four overhead bytes are used to implement the following features:

1. flow-control and corresponding buffering in both directions;

2. fragmentation and reassembling of data longer than the exchange area sizes;

3. synchronization of flow control numbers;

4. Service Access Point oriented communication;

5. Address Information;

6. Length Information.

Using No Flow Control, all the bytes of the PROFIBUS DP exchange areas are used

by the application layer. The input area is updated whenever a new reading event

must be transferred to the Master station. Since flow control is not implemented, the

Master station must be fast enough to get all the barcode events, reading the input

area before it changes due to a new barcode occurrence.

In addition, if application data is longer than input area sizes, data is automatically

truncated. Since the No Flow Control Mode does not require any particular

implementation at the Master side, in the following sections we will examine only the

flow controlled version. This will be referred to as Dynamic PROFIBUS Driver (DPD).