80C187 Datasheet, PDF (10/30 Pages) Intel Corporation – 80-BIT MATH COPROCESSOR

80C187
270640 – 4
Precision Control
Rounding Control
00 24 Bits (Single Precision)
00 Round to Nearest or Even
01 (Reserved)
01 Round Down (toward b %)
10 53 Bits (Double Precision)
10 Round Up (toward a %)
11 64 Bits (Extended Precision)
11 Chop (Truncate toward Zero)
The ‘‘infinity control’’ bit is not meaningful to the 80C187 To maintain compatibility with the 8087 this bit can be
programmed however regardless of its value the 80C187 treats infinity in the affine sense (b% ^k a %)
Figure 5 Control Word
15
IP_{19 16}
OP_{19 16}
7
0
CONTROL WORD
a0
STATUS WORD
a2
TAG WORD
a4
INSTRUCTION POINTER_{15 0}
a6
0
OPCODE_{10 0}
a8
OPERAND POINTER_{15 0}
aA
0 0 0 0 0 0 0 0 0 0 0 0 aC
Figure 6 Instruction and Data Pointer Image in Memory
10