指令BFLDH的用法?

[gorzen]

下面是BFLDH这条指令的详细描述,但是还是没太看懂,望各位前辈指点:
1)详细说明一下OP1,OP2,OP3各自的执行情况,最好能举例说明.
2)说明一下BFLDH这条指令的目的是干嘛?

BFLDH Bit Field High Byte
Syntax BFLDH op1, op2, op3
Operation (tmp) <-- (op1)
(high byte (tmp)) <-- ((high byte (tmp) ^ ¬op2) v op3)
(op1) <-- (tmp)
Data Types WORD
Description
Replaces those bits in the high byte of the destination word operand op1 which are selected by an ’1’ in
the AND mask op2 with the bits at the corresponding positions in the OR mask specified by op3.
Note: Bits which are masked off by a ’0’ in the AND mask op2 may be unintentionally altered if the corresponding
bit in the OR mask op3 contains a ’1’.

Flags
E Z V C N
0 * 0 0 *

E Always cleared.
Z Set if the word result equals zero. Cleared otherwise.
V Always cleared.
C Always cleared.
N Set if the most significant bit of the word result is set. Cleared otherwise.

[wgzh]

BFLDH op1, op2, op3

1)
OP2先取反然后与OP1的高字节相与,得到的值再与OP3相或结果存入OP1的高位.
也就是最终把OP3的为1的位赋值到OP1的高字节上去. OP1高字节其它位与OP2的取反后相与得到.
例: OP1 = 1234H; OP2 = 56H; OP3 = 80H;
OP2取反 为a9h; 与OP1的高字节12H相与=0; 结果与OP3相或=80H;
运算后OP1就等于8034H了
2)
BFLDH这条指令的目的就是给OP1的高字节的某位或某几位置一.