BECKHOFF BK2000 - Manual (Page 19)

Beckhoff-Lightbus coupler BK2000
BK2000 19
The contents "00" only enable "Page 0 READ accesses". In later master
versions, control bytes other than only "10hex" and "00hex" are also
possible. Access to Page 1 is enabled with the control byte "30hex". Page
0 contains process data, whereas Page 1 contains internal registers and
parameters of the bus coupler.
The data bytes D2 and D3 of the telegram serve to transport data out of
the memory and into the memory of the bus coupler. Access is always
word-oriented, and byte access is not possible. The connection between
the memory address and the periphery is described in the chapter entitled
"The periphery data in the process image".
To ensure data consistency, the bus coupler must be synchronized for
master access. The bus coupler is triggered to update the periphery by
means of three different mechanisms. The first possibility is to send the
following telegram:
Control
D0 D1 D2 D3
10hex FFhex 80hex xx Toggle, Info - Byte
An "update command" is triggered by modification of the data byte D3
(toggle byte, TGL), i.e. it is written with a changing pattern. The bus coupler
queries this address constantly and begins to update the inputs and
outputs after a change in the pattern. Once the update has been
successful, the bus coupler copies the toggle pattern out of the output
memory address 255 into the input memory. The master can query the bus
coupler's status by querying this memory address. The second byte at
address 255 is a status and info byte that contains information about the
bus coupler.
A further possibility of getting the bus coupler to run an update is to trigger
an interrupt, the "Int command". A memory cell with the address 255
Controll
D0 D1 D2 D3
30hex FFhex 80hex xx xx
is written and immediately triggers an interrupt in the bus coupler. The con-
tents of the memory cell are deleted by access of the bus coupler to this
cell. The contents can practically not be read back for as long as the bus
coupler is running in the interrupt routine.
The third possibility of sending the "update command" is particularly
interesting with regard to large systems. Here, a "BROADCAST telegram"
can be sent. This telegram causes all bus couplers in the ring to run an
update.
Controll
D0 D1 D2 D3
0Bhex FFhex 80hex xx xx
In the TwinCAT and S2000 software, access to the BK2000 bus coupler is
run automatically. Its operating principle is transparent to the user.
Diagnostic and
status functions
The extensive diagnostic functions of the Beckhoff-Lightbus enable swift
location of errors. The master is capable of determining the position of an
error. For error messages of the bus coupler or the bus terminals, the bus
coupler has registers in which the messages can be retrieved. The
diagnostic messages are accommodated in Page 1 of the bus coupler
(telegram with the control byte "30hex").
The following messages can be retrieved from Page 0 and Page 1 at the
address 255.