mc68hc705j2 Freescale Semiconductor, Inc, mc68hc705j2 Datasheet - Page 23

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mc68hc705j2

Manufacturer Part Number
mc68hc705j2
Description
8-bit Microcontroller
Manufacturer
Freescale Semiconductor, Inc
Datasheet
4.1.5.4 Zero Flag
4.1.5.5 Carry/Borrow Flag
4.2 Arithmetic/Logic Unit (ALU)
4.3 Addressing Modes
4.1.5.3 Negative Flag
MOTOROLA
4-4
The CPU sets the negative flag when an arithmetic operation, logical operation,
or data manipulation produces a negative result. Bit 7 of the negative result is
automatically set, so the negative flag can be used to check an often-tested bit
by assigning it to bit 7 of a register or memory location.
accumulator with the contents of that register or location then sets or clears the
negative flag according to the state of the tested bit.
The CPU sets the zero flag when an arithmetic operation, logical operation, or
data manipulation produces a $00.
The CPU sets the carry/borrow flag when an addition operation produces a
carry out of bit 7 of the accumulator.
manipulation instructions also clear or set the carry/borrow flag.
The ALU performs the arithmetic and logical operations defined by the
instruction set.
The binary arithmetic circuits decode instructions and set up the ALU for the
selected operation. Most binary arithmetic is based on the addition algorithm,
carrying out subtraction as negative addition. Multiplication is not performed as
a discrete operation but as a chain of addition and shift operations within the
ALU. The multiply instruction (MUL) requires 11 internal processor cycles to
complete this chain of operations.
The CPU uses eight addressing modes for flexibility in accessing data. These
addressing modes define the manner in which the CPU finds the data required
to execute an instruction. The eight addressing modes are as follows:
• Inherent
• Immediate
• Direct
• Extended
• Indexed, no offset
• Indexed, 8-bit offset
• Indexed, 16-bit offset
• Relative
CENTRAL PROCESSOR UNIT
Some logical operations and data
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MC68HC705J2

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