User's Manual

THE 80286 INSTRUCTION SET
CLTS-Clear Task Switched Flag
Opcode
Instruction
Clocks Description
OF 06 CLTS
2 Clear task switched flag
FLAGS MODIFIED
Task switched=O
FLAGS UNDEFINED
None
OPERATION
CLTS clears the task switched flag in the Machine Status Word. This flag is set by the 80286 every
time a task switch occurs. The TS flag
is used to manage processor extensions as follows: every execu-
tion of a WAIT or an ESC instruction
will be trapped if the MP flag of MSW is set and the task
switched flag
is set. Thus, if a processor extension is present and a task switch has been made since the
last
ESC instruction was begun, the processor extension's context must be saved before a new instruc-
tion can be issued. The fault routine
will save the context and reset the task switched flag or place the
task requesting the processor extension into a queue until the current processor extension instruction
is
completed.
CLTS appears in operating systems software, not in applications programs.
It is a privileged instruction
that can only be executed at level O.
PROTECTED MODE EXCEPTIONS
#GP(O) if CL TS is executed with a current privilege level other than o.
REAL ADDRESS MODE EXCEPTIONS
None (valid in REAL ADDRESS MODE to allow power-up initialization for Protected Mode) ,
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