Rockwell Automation 1771-IS 5V DC INPUT MOD - Manual (Page 35)

Programming and Operation
Chapter 3
3-16
Programming Example, PLC-2 Family
Two methods of programming are described: one using block transfer
instructions, the other using multiple GET instructions. Refer to
Figure 3.8. The data table mapping is the same for both.
For this example, 3 words of data are used to transfer the settings of two
4-digit thumbwheel switches. The settings are 9751 and 8642 for
thumbwheel switch assembly 1 and 2, respectively. (The first word is
reserved for diagnostic data.) The module is located in the upper slot of
rack 1 module group 2. The module address is 121
8
. If located in the
lower slot, the module address would be 120
8
and output bits 10, 11, 12,
16 and 17 used in the example would become 00, 01, 02, 06 and 07,
respectively.
Block Transfer Instructions
Rung 1 - When this rung is enabled, the switch status data in module
memory is transferred to the data table. The 3 words specified by the
block length will contain diagnostic data and the data of thumbwheel
switch assemblies 1 and 2.
The block length is set to 1 plus the number of thumbwheel switch
assemblies, or 1 plus the number of pairs of switch banks required by the
application.
Multiple Get Instructions
Read the description for BLOCK TRANSFER INSTRUCTIONS first.
Rung 1 - This rung is used to identify the module (module address 121
8
in the first GET instruction) and the first address of the destination of the
transferred data (word address 060
8
in the second GET instruction). The
rung also sets the block transfer read bit (bit 17) in the module’s output
image table byte.
Rungs 2, 3 - These rungs set the number of words to be transferred by
setting a binary bit pattern in the module’s output image table byte. Bits
10 and 11 are set ON. the binary bit pattern 11 is equivalent to the
number 3.