User's Manual

THE 80286 INSTRUCTION SET
JMP-Jump
Opcode Instruction
Clocks'
Description
EB cb JMP cb 7 Jump short
EA cd JMP cd 180 Jump to.task gate
E9 cw JMP cw 7
Jump near
EA cd JMP cd
11,pm=23
Jump far (4-byte immediate address)
EA cd JMP cd 38
Jump to
call gate, same privilege
EA cd
JMP cd
175
Jump via Task State Segment
FF
/4
JMP ew 7,mem=11 Jump near to EA word (absolute offset)
FF
/5
JMP ed 15,pm=26 Jump far (4-byte effective address in memory
doubleword)
FF
/5
JMP ed 41 Jump to call gate, same privilege
FF
/5
JMP
ed 178 Jump via Task State Segment
FF
/5
JMP
ed 183 Jump to task gate
'Add one
clock for every byte of the next instruction executed.
FLAGS MODIFIED
All if a task switch takes place; none if no task switch occurs.
FLAGS UNDEFINED
None
OPERATION
The JMP instruction transfers program control to a different instruction stream without recording any
return information.
For inter-segment jumps, the destination can be a code segment, a call gate, a task gate, or a Task
State Segment. The latter two destinations cause a complete task switch to take place.
Control transfers within a segment use the
JMP cw or JMP cb forms. The operand is a relative offset
added modulo 65536 to the offset of the instruction that follows the
JMP. The result is the new value
of
IP; the value of CS is unchanged. The byte operand is sign-extended before it is added; it can
therefore be used to address labels within
128 bytes in either direction from the next instruction.
Indirect jumps within a segment use the
JMP ew form. The contents of the register or memory operand
is an absolute offset, which becomes the new value of IP. Again, CS is unchanged.
Inter-segment jumps in real address mode simpiy set
IP to tile offset part of inl: iOIl!;; poilii,;;r .. iid ,,;; ..
CS to the selector part of the pointer.
In protected mode, inter-segment jumps cause the 80286 to consult the descriptor addressed by the
selector part of the long pointer. The
AR byte of the descriptor determines the type of the destination.
(See table
B-3 for possible values of the AR byte.) Following are the possible destinations:
1. Code segment-The addressability and visibility of the destination are verified, and CS and IP
are loaded with the destination pointer values.
B-56