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5 PLC
06.91
5.1 Structure
The PLC software for the computer link with SINUMERIK 8X0 consists of the PLC basic
software, the standard functions and the kernel sequences.
Processing in input direction:
If a message frame is addressed to a PLC, the COM area searches in the multiport RAM for a
free buffer to the PLC and stores the message frame data there.
If the data have been assessed to be valid, the PLC basic software accesses the input buffer
in the MPR (multiport RAM) and starts processing.
In case of a user message frame, the PLC basic software passes the message frame to the
user interface and sets a flag there, by means of which the user software recognizes that a
user message frame has arrived.
In case of a standard message frame, this is transmitted by the PLC basic software to the
processing program for standard functions. The processing result is communicated to the user
interface after the standard function has been processed.
Certain standard message frames are processed by kernel sequences.
Kernel sequences are fixed message frame sessions which cannot be changed by the PLC
user program.
Processing in output direction:
If a message frame is to be sent via the user interface, this is indicated to the PLC basic
software by means of a control flag. Then the PLC basic software copies the message frame
into the multiport RAM and informs the COM area that a message frame which is ready to be
sent is waiting in the multiport RAM.
If a standard message frame is to be output, this is communicated to the PLC in a specific
area of the user interface. Then processing and forwarding of the standard message frame is
effected automatically by the standard function blocks.
5–2
© Siemens AG 1989 All Rights Reserved
6FC5 197-0AB20-0BP0
SINUMERIK 840/880 (PJ)
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