Intel 80C188XL Arithmetic Interpretation of 8-Bit Numbers, Bit Manipulation Instructions, Shifts

OVERVIEW OF THE 80C186 FAMILY ARCHITECTURE

Table 2-5. Arithmetic Interpretation of 8-Bit Numbers

Hex	Bit Pattern	Unsigned	Signed	Unpacked	Packed
		Binary	Binary	Decimal	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

2.2.1.3Bit 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		“Not” byte or word
AND		“And” byte or word
OR		“Inclusive or” byte or word
XOR		“Exclusive or” byte or word
TEST		“Test” byte or word
		Shifts
SHL/SAL		Shift logical/arithmetic left byte or word
SHR		Shift logical right byte or word
SAR		Shift arithmetic right byte or word
		Rotates
ROL		Rotate left byte or word
ROR		Rotate right byte or word
RCL		Rotate through carry left byte or word
RCR		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 op- eration 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 bi- nary numbers by powers of two. Logical shifts can be used to isolate bits in bytes or words.

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