Intel 80386

COPROCESSOR HARDWARE INTERFACE
8086/87/88/186 MACRO ASSEMBLER Test for presence of B NlITIerics Chip, Revision 1.0
PAGE
lOC OBJ
OOlF 9BD9E8
0022 9BD9EE
0025 9BDEF9
0028 9BD9CO
002B 9BD9EO
002E 9BDED9
0031 9BD03C
0034 8B04
0036 9E
0037 7406
0039 EB0790
003C
003C EB0490
003F
003, EB0190
0042
0042
LINE
49
50
51
52
53
54
5"
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
ASSEMBLY COMPLETE, NO ERRORS FOUND
SOURCE
fldl
fldz
fdiv
fld st
fehs
fcOOW
fstsw [sil
mov DX,[Si]
sahf
je found_87_287
; Must use defaul t control Hord from FNINIT
; Form infinity
; 8087/287 says +;nf = -inf
; Form negative infinity
i 80387 says +;nf <> -inf
; See ; f they nre the same ond remove them
i look at gtatus from FCOHPP
; See if the infinities matched
; JlIIlP if 8087/287 is· present
An 80387 is present. If denorma l except i cns are used for an 8087/287,
they rust be masked. The 80387 will automatically normalize denormal
operands faster than an exception handler can.
j~ found_387
set up for no tJPX
j"" exit
found 87 287:
- ;;et up for 87/287
jrrp exit
found_387:
set up for 387
exit:
code ends
end
start,ds:dgroup,ss:dgroup:sst
Figure 5-4. Software Routine to Recognize the 80287 (Cont'd.)
5.4.2 80387 Emulator
G40107
The 80387 emulator circuit makes a lO-MHz 80287 appear to the 80386 as an 80387. The
schematic
is shown in Figure 5-5. An 80387 socket (80387 PGA Adapter) is connected to
the
80386 (connections not shown) as described earlier in this chapter. Please note that this
circuit
is provided to illustrate concepts only; it has not been tested.
The
80287 sends signals to the 80386 through the socket. The inputs coming to the socket
from the
80386 are decoded by the PAL16L8 (Math Control) to provide the buffered CMDO,
NPRD#,
and NPWR# inputs for the 80287. The PAL equations for the Math Control PAL
are listed in Appendix B of this manual.
The data lines of the
80287 are connected to the lower half of the 80386 data bus through
the socket; the
BUSY #, ERROR#, and PEREQ signals are returned to the 80386 through
the socket as well. Note
that while this circuit allows the 80386 to use an 80387 interface
with the
80287, the 80287 still performs only 16-bit data transfers. Therefore, during initial-
ization, the ERROR# output of the 80287 is high to indicate the presence of an 80287, not
an
80387.
5-10