Siemens SIMATIC TD 200, User Manual

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2-6
SIMATIC TD 200 Operator Interface
C79000-G7076-C272-01
Specifying Function Key Memory Bits and Display Update Rate
The dialog box shown in Figure 2-5 allows you to specify the internal memory byte
(M memory) address for the TD 200 function keys and determine the update rate
of the TD 200.
You must reserve eight bits of internal memory (M bits) for the TD 200 to use when
a function key is pressed. Your program can inspect these bits and take an action
when a key is pressed. One M bit is set by the TD 200 each time the
corresponding function key is pressed. Always reserve an M Area address even
when your program does not utilize function keys. Valid address values for specific
CPUs are defined in the
SIMATIC S7-200 Programmable Controller System
Manual.
!
Warning
The TD 200 sets an M bit each time a function key is pressed. If you do not intend
to use function keys, and therefore do not assign an M byte address for function
keys, the TD 200 defaults to byte M0 for the function keys. If your program uses
bits in M0, and a user presses any function key, the TD 200 sets the
corresponding bit in M0, overwriting the value assigned to that bit by your
program.
Inadvertent changes to M bits could cause your program to behave unexpectedly.
Unpredictable controller operation could cause death or serious injury to
personnel, and/or damage to equipment.
Always reserve an M area address, even when your program does not utilize
function keys.
Figure 2-4 shows a referenced byte (MBn) and shows which bit of the byte is set
by each function key.
F4 F3 F2 F1
Shift
F4
Shift
F3
Shift
F2
Shift
F1
MBn
MSB
7
6 5 4 3 2 1
LSB
0
Figure 2-4 Bits Set by Each Function Key
The update rate selection determines how often the TD 200 polls the S7-200 CPU
for messages to display. The actual update time may be slower than the time that
you select because of the size of the message, the processing required, or
network traffic.
Configuring the TD 200