Siemens SINUMERIK 840C Installation Instructions Manual page 1057

12 Functional Descriptions
12.28.2 Functional description
• It is possible to define in the PLC user program which data are to be transferred via a
maximum of 32 high-speed data channels.
• The minimum updating rate of these high-speed channels is identical to the set
interpolation cycle (in NC), but can be set to a high multiple of the interpolation cycle for
each individual channel in order to minimize unnecessary operating time loading of the NC.
• The user has the option of processing the updating rate in an interrupt- or time-controlled
DB (DB 3) in the PLC.
• A special "configuring channel" is provided to allow the high-speed data channels to be
configured (DB 2) in terms of the type and direction of the data to be transferred during
operation.
• Configuring measures can be taken to determine whether values should always be
updated or whether they should be updated only after the last value to be entered in the
high-speed channel has been read by the partner (NC or PLC) (channel operation with
acknowledgement). As from SW 4, several data channels can be controlled simultaneously
("Synchronous data channels").
• New configurations or re-configurations of this type are not processed in the interpolation
cycle, but in the 40 ms reference.
• Only one high-speed channel can ever be configured via the configuring channel.
• On successful completion of the configuration, the data channels can be activated
individually or jointly. All activated data channels become active immediately (i.e. in the
next IPO cycle at the latest) and simultaneously.
• Each individual high-speed data channel is capable of transferring a maximum of one 32-
bit value (the data length is specific to data group and data type). Since the processor is
not capable of writing/reading 32-bit data to/from the link RAM with one single access
operation, access must be co-ordinated between the NC and PLC by means of
semaphores in order to prevent incorrect data from being read. These semaphores are
used by the PLC only when 32-bit values are transferred by means of a high-speed
channel, but not for 8-bit or 16-bit data (in order to save program run times). The PLC user
should always use semaphores in order to guarantee programming consistency on the
PLC side and to eliminate programming errors in the user program. The assignment
between semaphores and high-speed data channels is 0:1, i.e. semaphore 0 controls the
data exchange via the 1st high-speed channel, semaphore 31 controls the data exchange
via the 32nd high-speed channel and so on. The log for configuration and use of the high-
speed data channels is established and is not assisted by function macros provided by
Siemens. It is the particular responsibility of the PLC user to make sure that semaphores
are always used.
• Since the NC interpolation cycle is not synchronized with PLC processing blocks, it cannot
be guaranteed that values read in a PLC processing block, which have been supplied by
several channels, all originate from the same IPO cycle.
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© Siemens AG 1992 All Rights Reserved
07.97
6FC5197- AA50
SINUMERIK 840C (IA)