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Q117865: DOCERR: Control and Status Word Missing Abbreviation Info

Article: Q117865
Product(s): Microsoft Macro Assembler
Version(s): 6.11
Operating System(s): 
Keyword(s): 
Last Modified: 04-MAY-2001

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The information in this article applies to:

- Microsoft Macro Assembler (MASM), version 6.11 
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SUMMARY
=======

Page 148 of the "MASM 6.11 Reference Manual" has an alphabetical listing of math
coprocessor instructions. Page 150 contains Figure 5.2, a diagram of the Control
Word and Status Word. The manual is missing the descriptions of the different
fields, which were included with the "MASM 6.0 Reference Manual."

The format of the Control-Word and Status-Word registers are as follows:

Control Word
------------

Bit                                          Bit
15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
X  X  X IC RC RC RC PC PC IE    PM UM ZM DM IM

Status Word
-----------

Bit                                          Bit
15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
B C3 ST ST ST C2 C1 C0 ES SF PE UE OE ZE DE IE

The abbreviations for the fields in the Control Word and Status Word are:

  IC - Infinity Control
  0 = Projective (default on 8087 and 80287)
  1 = Affine
  Note: Used for 8087 and 80287 only, 80387 uses affine regardless
        of setting

  RC - Rounding Control
  00 = Round to nearest or even (default)
  01 = Round down toward -infinity
  10 = Round up toward +infinity
  11 = Chop by truncating toward 0

  PC - Precision Control
  00 = 24-bit mantissa
  10 = 53-bit mantissa
  11 = 64-bit mantissa

  IE - Interrupt Enable Mask
  Used for 8087 only; undefined on 80287 and 80387

  SF - Stack Flag
  Used for 80387 only; undefined on 80287 and 8087

Exception Masks and Flags
-------------------------

  PM/PE - Precision
  UM/UE - Underflow
  OM/OE - Overflow
  ZM/ZE - Zero Divide
  DM/DE - Denormalized Operand
  IM/IE - Invalid Operation
  For masks:
     1 = masked; 0 = unmasked

  For exceptions:
     1 = exceptions; 0 = no exception
  B - Busy
  1 = exception control unit active

  C3 C2 C1 C0 - Condition Codes

  ST - Stack Top Pointer
  Points to current top of stack

  ES - Error Summary (80287/387)
  On a 8087, the value is IR - Interrupt Request

Additional query words: 6.11

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Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM611
Version           : :6.11

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