section 7 - Index of

SUB Subtract SUBOperation:O-S -4 D (parallel move)Assembler Syntax:SUB S,D (parallel move)Description: Subtract the source operand S from the destination operand 0 and storethe result in the destination operand O. Words (24 bits), long words (48 bits), and accumulators(56 bits) may be subtracted from the destination accumulator.Note: The carry bit is set correctly using word or long-word source operands if the extensionregister of the destination accumulator (A2 or B2) is the sign extension of bit 47 of thedestination accumulator (A or B). The carry bit is always set correctly using accumulatorsource operands.Example:SUB X1 ,A X:(R2)+N2,RO;24.;bit subtract, load RO, update R2Before ExecutionXi 1~ _________ $_OO_O_OO_3 __ ~A 1~ ___ $_OO_:O_OO_05_8_:24_2_42_4 __--'After ExecutionXii ~ _________ $_O_OO_OO_3 __ ~A~I ____ $_OO_:O_OO_05_5_:24_2_42_4 __ ~Explanation of Example: Prior to execution, the 24-bit X1 register contains the value$000003, and the 56-bit A accumulator contains the value $00:000058:242424. TheSUB instruction automatically appends the 24-bit value in the X1 register with 24 LSzeros, sign extends the resulting 48-bit long word to 56 bits, and subtracts the result fromthe 56-bit A accumulator. Thus, 24-bit operands are subtracted from the MSP portion ofA or B (A 1 or B1) because all arithmetic instructions assume a fractional, twos complementdata representation. Note that 24-bit operands can be subtracted from the LSP portionof A or B (AO or BO) by loading the 24-bit operand into XO or YO, forming a 48-bitword by loading X1 or Y1 with the sign extension of XO or YO, and executing a SUB X,Aor SUB Y,A instruction.