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Bitwise Operations Guide

The document discusses different types of operations that can be performed on bits in the status register including setting and clearing bits. It also discusses different types of shift instructions like logical, arithmetic, and rotation shifts. Finally, it covers flow of control instructions like branches, calls, returns and different types of jumps including unconditional and conditional jumps.

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52 views6 pages

Bitwise Operations Guide

The document discusses different types of operations that can be performed on bits in the status register including setting and clearing bits. It also discusses different types of shift instructions like logical, arithmetic, and rotation shifts. Finally, it covers flow of control instructions like branches, calls, returns and different types of jumps including unconditional and conditional jumps.

Uploaded by

dineshe.ece
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Operations on Bits in Status Register

• There is a set of emulated instructions to set or clear


the four lowest bits in the status register and these can
be masked using the constant generator.
• Ex: clrc ; clear carry bit.
• clrn ; clear negative bit.
• clrz ; clear zero bit.
• setc ; set carry bit.
• setn ; set negative bit.
• setz ; set zero bit.
• dint ; disable general interrupts.
• eint ; enable general interrupts.
Shift and Rotate Instructions
• There are three types of shifts
(i) logical shift (ii) arithmetic shift (iii)
rotation. They are explained below.
Contd…
• Logical shift inserts zeroes for both right and left
shifts.
• Arithmetic shift inserts zeroes for left shifts but
the most significant bit, which carries the sign, is
replicated for right shifts.
• Rotation does not introduce or lose any bits; bits
that are moved out of one end of the register are
passed around to the other.
• Ex : rla dst ; arithmetic shift left
• rra src ; arithmetic shift right.
• rlc dst ; rotate left through carry.
• rrc src ; rotate right through carry
Flow of Control
• The most common elementary use of call is
for a subroutine that begins at a particular
label.
• Ex: br src ; branch (go to).
• call src ; call subroutine.
• ret ; return from subroutine.
• reti ; return from interrupt.
• nop ; no operation (consumes single cycle)
Jumps(Unconditional and Conditional)
• jmp fits in a single word, including the offset,
but its range is limited to about 1KB from the
current location.
• jmp label ; unconditional jump.
Contd…
• The conditional jumps are the “decision-
making” instructions and test certain bits or
combinations in the status register.
• Ex : jc label ; jump if carry set
• jnc label ; jump if carry not set ,
• jn label ; jump if negative ,
• jz label ; jump if zero
• jnz label ; jump if nonzero.
• jge label ; jump if greater or equal ,
• jl(t) label ; jump if less than

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