參數(shù)資料
型號(hào)： Intel387 dx
廠商： Intel Corp.
英文描述： DX Math Coprocessor(32位數(shù)學(xué)協(xié)處理器)
中文描述： 霉素?cái)?shù)學(xué)協(xié)處理器（32位數(shù)學(xué)協(xié)處理器）
文件頁(yè)數(shù)： 9/41頁(yè)
文件大小： 406K
代理商： INTEL387 DX
Intel387
TM
DX MATH COPROCESSOR
240448–3
ES is set if any unmasked exception bit is set; cleared otherwise.
See Table 2.2 for interpretation of condition code.
TOP values:
000
e
Register 0 is Top of Stack
001
e
Register 1 is Top of Stack
#
#
111
e
Register 7 is Top of Stack
For definitions of exceptions, refer to the section entitled
‘‘Exception Handling’’
Figure 2.2. MCP Status Word
2.3.3 STATUS WORD
The 16-bit status word (in the status register) shown
in Figure 2.2 reflects the overall state of the MCP. It
may be read and inspected by CPU code.
Bit 15, the B-bit (busy bit) is included for 8087 com-
patibility only. It reflects the contents of the ES bit
(bit 7 of the status word), not the status of the
BUSY
Y
output of the Intel387 DX MCP.
Bits 13–11 (TOP) point to the Intel387 DX MCP reg-
ister that is the current top-of-stack.
The four numeric condition code bits (C
3
–C
0
) are
similar to the flags in a CPU; instructions that per-
form arithmetic operations update these bits to re-
flect the outcome. The effects of these instructions
on the condition code are summarized in Tables 2.2
through 2.5.
Bit 7 is the error summary (ES) status bit. This bit is
set if any unmasked exception bit is set; it is clear
otherwise. If this bit is set, the ERROR
Y
signal is
asserted.
Bit 6 is the stack flag (SF). This bit is used to distin-
guish invalid operations due to stack overflow or un-
derflow from other kinds of invalid operations. When
SF is set, bit 9 (C
1
) distinguishes between stack
overflow (C
1
e
1) and underflow (C
1
e
0).
Figure 2.2 shows the six exception flags in bits 5–0
of the status word. Bits 5–0 are set to indicate that
the MCP has detected an exception while executing
an instruction. A later section entitled ‘‘Exception
Handling’’ explains how they are set and used.
Note that when a new value is loaded into the status
word by the FLDENV or FRSTOR instruction, the
value of ES (bit 7) and its reflection in the B-bit (bit
15) are not derived from the values loaded from
memory but rather are dependent upon the values of
the exception flags (bits 5–0) in the status word and
their corresponding masks in the control word. If ES
is set in such a case, the ERROR
Y
output of the
MCP is activated immediately.
9
9
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