80C186EC/80C188EC Microprocessor User's Manual

OVERVIEW OF THE 80C186 FAMILY ARCHITECTURE
Table 2-5. Arithmetic Interpretation of 8-Bit Numbers
Hex
Bit Pattern
Unsigned
Binary
Signed
Binary
Unpacked
Decimal
Packed
Decimal
07 0 0 0 0 0 1 1 1 7 +7 7 7
89 1 0 0 0 1 0 0 1 137 –119 invalid 89
C5 1 1 0 0 0 1 0 1 197 –59 invalid invalid
2.2.1.3 Bit Manipulation Instructions
There are three groups of instructions for manipulating bits within bytes and words. These three
groups are logical, shifts and rotates. Table 2-6 lists the bit manipulation instructions and their
functions.
Table 2-6. Bit Manipulation Instructions
Logicals
NOT
AND
OR
XOR
TEST
“Not” byte or word
“And” byte or word
“Inclusive or” byte or word
“Exclusive or” byte or word
“Test” byte or word
Shifts
SHL/SAL
SHR
SAR
Shift logical/arithmetic left byte or word
Shift logical right byte or word
Shift arithmetic right byte or word
Rotates
ROL
ROR
RCL
RCR
Rotate left byte or word
Rotate right byte or word
Rotate through carry left byte or word
Rotate through carry right byte or word
Logical instructions include the Boolean operators NOT, AND, OR and exclusive OR (XOR), as
well as a TEST instruction. The TEST instruction sets the flags as a result of a Boolean AND operation
but does not alter either of its operands.
Individual bits in bytes and words can be shifted either arithmetically or logically. Up to 32 shifts
can be performed, according to the value of the count operand coded in the instruction. The count
can be specified as an immediate value or as a variable in the CL register. This allows the shift
count to be a supplied at execution time. Arithmetic shifts can be used to multiply and divide binary
numbers by powers of two. Logical shifts can be used to isolate bits in bytes or words.
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