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Shift Instructions Section 5-17
5-17-10 ASYNCHRONOUS SHIFT REGISTER – ASFT(17)
Limitations St and E must be in the same data area, and E must be greater than or equal
to St.
DM 6144 to DM 6655 cannot be used for St or E.
Description When the execution condition is OFF, ASFT(17) does nothing and the pro-
gram moves to the next instruction. When the execution condition is ON,
ASFT(17) is used to create and control a reversible asynchronous word shift
register between St and E. This register only shifts words when the next word
in the register is zero, e.g., if no words in the register contain zero, nothing is
shifted. Also, only one word is shifted for each word in the register that con-
tains zero. When the contents of a word are shifted to the next word, the origi-
nal word’s contents are set to zero. In essence, when the register is shifted,
each zero word in the register trades places with the next word. (See Example
below.)
The shift direction (i.e. whether the “next word” is the next higher or the next
lower word) is designated in C. C is also used to reset the register. All of any
portion of the register can be reset by designating the desired portion with St
and E.
Control Word Bits 00 through 12 of C are not used. Bit 13 is the shift direction: turn bit 13
ON to shift down (toward lower addressed words) and OFF to shift up (toward
higher addressed words). Bit 14 is the Shift Enable Bit: turn bit 14 ON to
enable shift register operation according to bit 13 and OFF to disable the reg-
ister. Bit 15 is the Reset bit: the register will be reset (set to zero) between St
and E when ASFT(17) is executed with bit 15 ON. Turn bit 15 OFF for normal
operation.
Note If the non-differentiated form of ASFT(17) is used, data will be shifted every
cycle while the execution condition is ON. Use the differentiated form to pre-
vent this.
Flags ER: The St and E words are in different areas, or St is greater than E.
Indirectly addressed EM/DM word is non-existent.
(Content of *EM/*DM word is not BCD, or the EM/DM area boundary
has been exceeded.)
ASFT(17)
C
St
E
Ladder Symbols
@ASFT(17)
C
St
E
C: Control word
IR, SR, AR, DM, EM, HR, LR, #
St: Starting word
IR, SR, AR, DM, EM, HR, LR
E: End word
IR, SR, AR, DM, EM, HR, LR
Operand Data Areas
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