Bus Interface Profibus-Dp - Balluff BIS C-60 2 Serie Handbuch

C60_2-028_823024_0401-e.p65
11
Initializing the
data carrier
(continued)
An address named
in a telegram does
not distinguish be-
tween data carriers
with and without
initialization.
Control Function
12
PROFIBUS-DP
12 E
BIS C-60_2 Processor
Optimized data carrier memory management
Example of an initialization:
On a data carrier with 128 byte memory size, 24 bytes shall be used for reading and writing.
The maximum permissible number of write cycles according to the data carrier data sheet is
100,000. The result is the following initialization of the first 9 bytes of memory:
Number of the 1st memory range
Memory size of data carrier 128 bytes
Permissible no. of write cycles 100,000
Maximum no. of bytes per read/write cycle
set to 24 bytes
Counter of 1st field set to 0
The ratio of memory size to memory requirement thus permits 400,000 write cycles, since the
available memory size can be divided into 4 memory ranges of 100,000 bytes each. The pre-
warning is given after the 399,000th write cycle.
The processor writes data from the host system to the data carrier or reads data from the tag
through the read/write head and prepares it for the host system. Host systems may include:
– a host computer (e.g. industrial PC) or
– a programmable logic controller (PLC)

BUS interface PROFIBUS-DP

Communication between the BIS C-60_2 processor and the host system is via PROFIBUS-DP.
The PROFIBUS-DP system consists of the components:
– the bus master and
– the bus modules/slaves (here the BIS C-60_2 processor).
Important hints for use with PLC:
In some control systems the PROFIBUS-DP data area is not synchronously transmitted with the
updating of the input/output content. If more than 2 bytes of data are sent, a mechanism must
be used which guarantees that the data in the PLC and the data in the BIS C are always identi-
cal!
1st alternative: Synchronous data transmission as a setting on the Master
In this method the bus Master ensures that all the data necessary for the respective Slave are
always sent contiguously. There is usually a special software function in the PLC which likewise
controls access between the PLC and bus Master so that data are always sent contiguously.
2nd alternative: Set 2nd bit header
Data exchange between PLC and BIS is controlled by the so-called bit header. This is always
the first byte of the respective read/write head in the data buffer. This bit header exists both in
the input range (data from BIS to the PLC) and in the output range (data from the PLC to the
BIS). lIf this bit header is also sent as the last byte, a comparison of these two bytes can be
used to guarantee the consistency of the transmitted data.
In this method the PLC cycle is unaffected nor is the bus access time changed. All that is
required is that a byte in the data buffer be used for the 2nd bit header instead of for user data.
This 2nd alternative is the Balluff recommended setting (factory default).
00 01 01 00 18 00 00 00
H H H H H H H
00
H H
E 11