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OVERVIEW OF THE 80C186 FAMILY ARCHITECTURE
2-20
Table 2-5 shows the interpretations of various bit patterns according to number type. Binary num-
bers can be 8 or 16 bits long. Decimal numbers are stored in bytes, two digits per byte for packed
decimal and one digit per byte for unpacked decimal. The processor assumes that the operands in
arithmetic instructions contain data that represents valid numbers for that instruction. Invalid data
may produce unpredictable results. The Execution Unit analyzes the results of arithmetic instruc-
tions and adjusts status flags accordingly.
Table 2-4. Arithmetic Instructions
Addition
ADD Add byte or word
ADC Add byte or word with carry
INC Increment byte or word by 1
AAA ASCII adjust for addition
DAA Decimal adjust for addition
Subtraction
SUB Subtract byte or word
SBB Subtract byte or word with borrow
DEC Decrement byte or word by 1
NEG Negate byte or word
CMP Compare byte or word
AAS ASCII adjust for subtraction
DAS Decimal adjust for subtraction
Multiplication
MUL Multiply byte or word unsigned
IMUL Integer multiply byte or word
AAM ASCII adjust for multiplication
Division
DIV Divide byte or word unsigned
IDIV Integer divide byte or word
AAD ASCII adjust for division
CBW Convert byte to word
CWD Convert word to double-word