80C187
80C187 EXTENSIONS TO THE CPU’s
INSTRUCTION SET
Instructions for the 80C187 assume one of the five
forms shown in Table 12. In all cases, instructions
are at least two bytes long and begin with the bit
pattern 11011B, which identifies the ESCAPE class
of instruction. Instructions that refer to memory oper-
ands specify addresses using the CPU’s addressing
modes.
MOD (Mode field) and R/M (Register/Memory spec-
ifier) have the same interpretation as the corre-
sponding fields of CPU instructions (refer to Pro-
grammer’s Reference Manual for the CPU). The
DISP (displacement) is optionally present in instruc-
tions that have MOD and R/M fields. Its presence
depends on the values of MOD and R/M, as for in-
structions of the CPU.
The instruction summaries that follow assume that
the instruction has been prefetched, decoded, and is
ready for execution; that bus cycles do not require
wait states; that there are no local bus HOLD re-
quests delaying processor access to the bus; and
that no exceptions are detected during instruction
execution. Timings are given in internal 80C187
clocks and include the time for opcode and data
transfer between the CPU and the NPX. If the in-
struction has MOD and R/M fields that call for both
base and index registers, add one clock.
Table 12. Instruction Formats
Instruction
Optional
First Byte Second Byte Field
1 11011 OPA 1 MOD 1 OPB R/M DISP
2 11011 MF OPA MOD OPB * R/M DISP
3 11011 d P OPA 1 1 OPB * ST (i)
4 11011 0 0 1 1 1 1 OP
5 11011 0 1 1 1 1 1 OP
15–11 10 9 8 7 6 5 4 3 2 1 0
NOTES:
OP
e
Instruction opcode, possibly split into two fields OPA and OPB
MF
e
Memory Format
00Ð 32-Bit Real
01Ð 32-Bit Integer
10Ð 64-Bit Real
11Ð 16-Bit Integer
d
e
Destination
0Ð Destination is ST(0)
0Ð Destination is ST(i)
R XOR d
e
0Ð Destination (op) Source
R XOR d
e
1Ð Source (op) Destination
*In FSUB and FDIV, the low-order bit of OPB is the R (reversed) bit
P
e
Pop
0Ð Do not pop stack
1Ð Pop stack after operation
ESC
e
11011
ST(i)
e
Register Stack Element
i
000
e
Stack Top
001
e
Second Stack Element
#
#
#
111
e
Eighth Stack Element
27
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