Chapter
13
131
Shift Register Instructions
The file shift instructions are:
Shift File Up
Shift File Down
FIFO
Load
FIFO
Unload
The first two output instructions are used to construct synchronous word
shift registers from 1 to 999 words long (Figure 13.1). Upon false-true
transition of rung decision, the data from input word will be shifted into
the file, and the data in the last/first word of the file will be shifted
up/down into the output word.
Figure 13.1
Example of a 64 Word SHIFT FILE UP/DOWN Register Starting at
Word 400
8
400
477
120
Input Addr
500
Output Addr
Shift Up
Shift Up
400
477
500
Output Addr
120
Input Addr
Shift Down
Shift Down
(A.)
(B.)
Shift up and shift down imply motion toward higher and
lower numbered data table addresses respectively.
13.0
General
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