Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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     15                     8   7                    0
     ┌──┬──┬──┬──┬──┬──┬──┬──┐┌──┬──┬──┬──┬──┬──┬──┬──┐
     │  │  │        │  │  │  ││  │  │  │  │  │  │  │  │
     │B │C3│   ST   │C2│C1│C0││ES│SF│PE│UE│OE│ZE│DE│IE│◄── Status word
     │  │  │        │  │  │  ││IR│  │  │  │  │  │  │  │
     └──┴──┴──┴──┴──┴──┴──┴──┘└──┴──┴──┴──┴──┴──┴──┴──┘
 
     B──Busy
       1 if exception control unit active
 
     C3, C2, C1, and C0──Condition codes
       The high byte can be loaded into processor flags with
       SAHF instruction. Coprocessor flags line up with
       processor flags as shown below:
 
        15                    8
       ┌──┬──┬──┬──┬──┬──┬──┬──┐
       │  │C3│  │  │  │C2│C1│C0│◄── Coprocessor
       └──┴──┴──┴──┴──┴──┴──┴──┘
 
         7                    0
       ┌──┬──┬──┬──┬──┬──┬──┬──┐
       │SF│ZF│  │AF│  │PF│  │CF│◄── Processor
       └──┴──┴──┴──┴──┴──┴──┴──┘
 
     ST──Stack Top Pointer
       Number (0 to 7) of register at current top of stack.
 
     ES/IR──Interrupt Request or Error Summary
       On 8087 1 if interrupt request
       On 80287, 80387, or 80486, 1 if any exception
 
     SF──Stack Flag
       On 80387 or 80486, 1 if stack overflow or underflow
       On 8087 and 80287, undefined
 
     Exception Flags
       PE = 1 if precision exception
       UE = 1 if underflow exception
       OE = 1 if overflow exception
       ZE = 1 if zero divide exception
       IE = 1 if invalid operation exception
 
     See also: Coprocessor Control Word, Coprocessor Environment
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