INSTRUCTION DESCRIPTIONS
A - 270 INSTRUCTION SET DETAILS MOTOROLA
Operation: Assembler Syntax:
D–S–C ➞ D (parallel move) SBC S,D (parallel move)
Description: Subtract the source operand S and the carry bit C of the condition code
register from the destination operand D and store the result in the destination accumula-
tor. Long words (48 bits) may be subtracted from the (56-bit) destination accumulator.
Note: The carry bit is set correctly for multiple-precision arithmetic using long-word oper-
ands if the extension register of the destination accumulator (A2 or B2) is the sign exten-
sion of bit 47 of the destination accumulator (A or B).
Example: :
MOVE L:<$0,X ;get a 48-bit LS long-word operand in X
MOVE L:<$1,A ;get other LS long word in A (sign ext.)
MOVE L:<$2,Y ;get a 48-bit MS long-word operand in Y
SUB X,A L:<$3,B ;sub. LS words; get other MS word in B
SBC YB A10,L:<$4 ;sub. MS words with carry; save LS dif.
MOVE B10,L:<$5 ;save MS difference
:
SBC Subtract Long with Carry SBC
Before Execution After Execution
A$00:000000:000000
X X
$800000:000000 $800000:000000
$00:800000:000000
A
B B
$00:000000:000003 $00:000000:000001
Y Y
$000000:000001 $000000:000001