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Data Shift Instructions Section 3-8
Description NASL(580) shifts D (the shift word) by the specified number of binary bits
(specified in C) to the left (from the rightmost bit to the leftmost bit). Either
zeros or the value of the rightmost bit will be placed into the specified number
of bits of the shift word starting from the rightmost bit.
Flags
Precautions For any bits which are shifted outside the specified word, the contents of the
last bit is shifted to the Carry Flag (CY), and all other data is lost.
When the number of bits to shift (specified in C) is “0,” the data will not be
shifted. The appropriate flags will turn ON and OFF, however, according to
data in the specified word.
When the contents of the control word C is out of range, an error will be gen-
erated and the Error Flag will turn ON.
If as a result of the shift the contents of D is 0000 hex, the Equals Flag will
turn ON.
If as a result of the shift the contents of the leftmost bit of D is 1, the Negative
Flag will turn ON.
Examples When CIO 0.00 is ON, The contents of CIO 1000 is shifted 10 bits to the left
(from the rightmost bit to the leftmost bit). The number of bits to shift is speci-
fied in bits 0 to 7 of word CIO 2000 (control data). The contents of bit 0 of
CIO 1000 is copied into bits from which data was shifted and the contents of
the rightmost bit which was shifted out of range is shifted into the Carry Flag
(CY). All other data is lost.
Index Registers ---
Indirect addressing
using Index Registers
,IR0 to ,IR15
–2048 to +2047 ,IR0 to –2048 to +2047 ,IR15
DR0 to DR15, IR0 to IR15
,IR0+(++) to ,IR15+(++)
,–(– –)IR0 to, –(– –)IR15
Area D C
Shift n-bits
Contents of "a" or "0" shifted in
N bits
Lost
Name Label Operation
Error Flag ER ON when the control word C (the number of bits to shift) is
not within range.
OFF in all other cases.
Equals Flag = ON when the shift result is 0.
OFF in all other cases.
Carry Flag CY ON when 1 is shifted into the Carry Flag (CY).
OFF in all other cases.
Negative Flag N ON when the leftmost bit is 1 as a result of the shift.
OFF in all other cases.
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