Siemens SINUMERIK 840C Installation Instructions Manual page 1068

09.95
12.28.8 Overview of function identifiers and configuring parameters (DB 2, DR 2 ... DR 6)
The data to be read are selected via configuring parameter 2. The following table shows the
available data options:
Configuring
parameter 2
10 Outputs of mixed I/O modules in NCK (4 bytes)
111 Inputs of first mixed I/O module in NCK (2 bytes)
112 Inputs of second mixed I/O module in NCK (2 bytes)
180 Inputs of Central Service Board (6 bits)
90 Special signals from NC to PLC
190 Special signals from PLC to NC (Note: The PLC can only write these data!)
Special signals; NC PLC
The user specifies in NC-MD 312-317 the location to which the NC should signal that an
emergency retraction has been initiated by a channel or axis, i.e. whether the NC outputs this
status information to a mixed I/O module or supplies it in the form of a special signal for the
PLC (MD 312-317 must then be set to a value between 91 and 94).
Special signals: PLC NC
The user also specifies in NC-MD 318-323 the location from which the NC accepts the
command to initiate emergency retraction (a value of between 91 and 94 indicates the special
signals from the PLC should be accepted).
Initialization/power-up/reaction to errors
The contents of the two data blocks DB2 and DB3 are erased by the NC software after NCK
power ON. The NC also erases all 32 semaphores in the link RAM to the PLC during power-
up. The high-speed data channels do not remain active after mains on/off since the data in the
NC are stored in the dynamic RAM. In addition, the NC-internal pointers must be re-calculated
after every power-up since, for example, changes to internal address lists may have occurred
as a result of the cancellation of axes by means of a power ON operation. The PLC user
program must re-configure the high-speed data channels after every link bus reset (i.e. also
after NCK power ON initiated by means of operator input or PLC cold restart). Since the PLC
generally executes a warm restart rather than a cold restart, it must be noted that the user
program operates with incorrect values (0) for a maximum of one cycle after a power ON
operation. The contents of the two data blocks are erased before the NC and PLC system
software is synchronized. Since the configuration of the high-speed data channels involves
several cycles, it must be not be defined in OB20.
It is advisable to use OB20 to divide up the high-speed data channels (see also application
example).
In the case of failure of the PLC sign-of-life monitoring function (alarm 43 "PLC-CPU not
ready"), the NC stops writing values into the link RAM. In the case of drive failure, drive data
read via the high-speed data channel are invalid (error identifier in data channel). The PLC can
detect a drive failure by monitoring the "Drive ready" signal. When the drive is connected
(again), the read drive data become valid again (NC resets error bit on next transmission of
data).
© Siemens AG 1992 All Rights Reserved
SINUMERIK 840C (IA)
Addressed data
6FC5197- AA50
12 Functional Descriptions
12–293