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5–6
Single Transfer Programming
Output
Word 016
Input
Word 116
Publication 1771 UM006B-EN-P - June 2002
Bidirectional single transfer programming, then, requires both an
input image table and an output image table word. The addresses of
these image table words depend on the location of the I/O module in
the chassis. For example, for modules in I/O rack 1, module group
6, the corresponding output image table word is 016; the input image
table word is 116. Because the encoder/counter module occupies
one module group in the I/O chassis, the processor writes one
complete 16-bit output image table word to the module and reads
one complete 16-bit input image table word from the module during
each I/O scan. Figure 5.4 shows the relationship of module slot
placement to image table location in memory.
Figure 5.4
Example Module Position/Image Table Word Relationship
Output Word
Written to Module (16 bits)
Input Word
Read from Module (16 Bits)
The input image table word, the means for reading data from the
module, is updated automatically by the processor each I/O scan. To
examine the input status word from the module, the program only
needs to examine the word stored at the input image table location
corresponding to the placement of the encoder/counter module.
The output image table word, the means for writing data to the
module, is sent by the processor automatically, each I/O scan. In
applications where only the output control word is used, this word
can be stored directly in the output image table location
corresponding to the placement of the encoder/count module.
Section titled Example Rungs-No Preset Words Used shows the
type of program needed for this type of communication.
Encoder/Counter Module
in I/O Rack No. 1
Module Group No. 6
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