Siemens SINUMERIK 840 Planning Manual page 86

5 PLC
5.1.1 User interfaces
In the following, data transfer from the input/output buffer of the multiport RAM to the user
interface and vice versa is described:
Input buffer user interface (figure "Transfer to user interface")
MPR
COM
O
I
O
I
O
I
O
I
O
I
O
I
Transfer to user interface
The PLC cyclically checks the 6 input buffers in the multiport RAM for incoming message
frames. Assignment of the input/output buffers is dynamic, i.e. there is no fixed allocation
between the buffers and the user interfaces. If valid data is in an input buffer, the buffer
processing program checks whether the message frame is to be processed by the
corresponding PLC and makes a distinction between configurable and standard message
frames. In the case of configurable message frames, it checks whether the addressed user
interface is free, i.e. whether the data can be copied.
If the user interface is free, the function number, the 6th to 8th character of the identification
(identification structure see Section 6, Message frames), the error number (9th and 10th
character) and the reference to the useful data from the input buffer are entered into that user
interface in data block 101.
The useful data are then copied into the specified data block (DB/DX).
After all data has been copied, the acknowledgement signal for the user interface is set and
the input buffer in the multiport RAM is acknowledged. The user has to release the user
interface by resetting the acknowledgement signal after he/she has initiated all necessary
responses to the incoming message frame.
5–4
PLC
PLC
User
OS
© Siemens AG 1989 All Rights Reserved
08.89
User
interface input
DB101
Acknowl.sig.
Identific. DB,DX
Fct.no. Id6
Id7 Id8
Error no.
DB/DX DW no.
Useful data DB/DX
Useful data length
Useful data
6FC5 197-0AB20-0BP0
SINUMERIK 840/880 (PJ)