Pretransmit - Bosch Rexroth ID 40 Manual

42/176 Accessing data on the ID 40/MDT
Bosch Rexroth AG, MIT: ID 40, 3 842 530 344/2014-05
PROOF COPy 1 | 20.05.2014 | FOR INTERNAL USE ONLy
6.4.1.2 Buffered prefetch
With buffered prefetch, the data read from the mobile data tag with the
parameterized read commands are stored in a special buffer in the SLK. The data
from multiple, consecutive read commands is entered in order of execution in the
buffer without interruption. This means, for example, that unrelated data areas can
be read from the mobile data tag and copied from the SLK in one related data block.
The control system can read some or all of this data buffer at any time, even if the
MDT has already left the HF field of the SLK. The data in the buffer remains valid
until it is overwritten by a subsequent MDT.
The maximum buffer size corresponds to the current MDT size. This means the entire
contents of an ID 40/MDT32K can be read with buffered prefetch.
The parameterized data blocks cannot exceed the address area of the MDT.
Otherwise, the wrong data bytes are flagged in the prefetch buffer, and an error
code is returned when reading the buffer.
6.4.2

Pretransmit

Pretransmit refers to any parameterized write access to the mobile data tag. These
write commands are divided into those executed only once and those executed for
each additional MDT.
Setting the parameters of a pretransmit means entering SLK addresses together
with the data that should be written starting with the addresses.
The pretransmit data block is entered in the SLK through a fieldbus command. Other
commands add data blocks and the address ranges of these data blocks can also
overlap.
Configuring the pretransmit means:
• Selecting whether the pretransmit should be executed as a single transmit or a
multiple transmit
• Releasing the pretransmit for execution. As long as the pretransmit is locked,
additional data blocks in the SLK can be entered without a present MDT with
incomplete pretransmit data being written.
• Established pretransmits can also be deleted.
Pretransmit always occurs before prefetch in the PRECONNECTED state.
It is recommended to only execute a pretransmit with stopped workpiece pallets,
since otherwise the dwell time of the MDT in the field is too brief to transfer the
amount of data through the field.
If an error occurs during pretransmit (e.g., the amount of data parameterized for
the MDT is too large), the bytes not transmitted are flagged in the SLK. This can be
verified by subsequent read access to the pretransmit data block. Since there is
no bus communication during pretransmit, errors cannot be reported through the
fieldbus.