Direct And Parameterized Data Transmission; Securing Data Transmission - Bosch Rexroth ID 40 Manual

22/176 Introduction
Bosch Rexroth AG, MIT: ID 40, 3 842 530 344/2014-05
PROOF COPy 1 | 20.05.2014 | FOR INTERNAL USE ONLy
2.3.3

Direct and parameterized data transmission

The data on the mobile data tag can be accessed directly as long as the MDT is
located within the HF field of the read/write head. To do this, the control system
sends read and write commands to the read/write head through the fieldbus. The
read/write head executes these commands immediately and reports the result to the
control system.
For parameterized data transmissions, the control system sends the read and write
commands to the read/write head when there is no mobile data tag in the HF field.
These commands are buffered in the read/write head and automatically executed
when an MDT enters the HF field. These commands are divided into those executed
only once and those executed for each additional MDT.
Parameterized data transmissions are particularly quick, since the read and write
commands are already stored in the SLK. This makes them best suited for dynamic
reading and writing.
Direct and parameterized data transmissions can also be combined. When an MDT
enters the HF field, all parameterized commands are executed first, followed by the
direct data transmission.
2.3.4

Securing data transmission

The data between the SLK and MDT is sent and received wirelessly via an HF field.
Checksums are used to monitor the transmission of data without errors. To do
this, each data packet contains redundant parity bits, known as longitudinal and
transverse parities. If the system detects a transmission error, the sent data packets
are resent to ensure secure communication between the SLK and the MDT.
The MDT is also sent a special data package, known as the sign-off sequence,
to indicate the end of the data transmission. If the MDT leaves the HF field of
the SLK without signing off first, a communication error is entered in the MDT
status register. The SLK itself registers the MDT's unexpected departure with a
corresponding error state (see Chapter 6.9 "MDT lifeguarding").
If no data on the MDT was altered, an error is not registered even though
communication is interrupted unexpectedly.