Assembly 如何在8051汇编编程中计算指令的大小（添加一个，Rn-->；1字节..？）？

我是汇编编程新手

ADD A,Rn

是1字节指令和

ADD A,direct

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是2字节指令。为什么？

添加一个，Rn

可以将操作码+寄存器号编码为一个单独的字节，因此是1字节指令

有8种不同的操作码保存在1个字节上，由以下部分组成：

base_operand = 0x28 (only 6 bits are required)
R_register_index = 0->7 (only 3 bits are required)

instruction = base operand OR R_register_index

ADD A,R0    0x28
ADD A,R1    0x29
ADD A,R2    0x2A
ADD A,R3    0x2B
ADD A,R4    0x2C
ADD A,R5    0x2D
ADD A,R6    0x2E
ADD A,R7    0x2F

ADD A，direct

需要一个字节用于操作码，至少另一个字节用于保存参数，这解释了大小>1的原因（例如：

MOV RO，#12H

：2个字节）

指令大小的范围为1到3字节，但对于指令的大小没有绝对的规则。（对于带有2个参数的某些指令，请从内存中读取）

最好检查你在内存中得到所有指令和它们的大小的参考

计算大小更可靠的方法是构建指令大小表（IST）：操作码=>size

调试器就是这样“预测”下一个指令地址的

为了完整起见，让我向您提供此表（请注意，

$A5

是保留的，不是说明：我将大小设置为0）

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在大多数情况下，1字节用于操作码，1字节用于#数据，1字节用于地址或相对地址

---

谢谢

它如何将MOV A、Rn编码为一个字节…请添加参考资料，我可以从中获得详细解释。。？？提前感谢，我已经编辑了我的帖子，专门解释了MOV A，Rn编码。谢谢你接受答案。

op     sz
$00 => 1
$01 => 2
$02 => 3
$03 => 1
$04 => 1
$05 => 2
$06 => 1
$07 => 1
$08 => 1
$09 => 1
$0A => 1
$0B => 1
$0C => 1
$0D => 1
$0E => 1
$0F => 1
$10 => 3
$11 => 2
$12 => 3
$13 => 1
$14 => 1
$15 => 2
$16 => 1
$17 => 1
$18 => 1
$19 => 1
$1A => 1
$1B => 1
$1C => 1
$1D => 1
$1E => 1
$1F => 1
$20 => 3
$21 => 2
$22 => 1
$23 => 1
$24 => 2
$25 => 2
$26 => 1
$27 => 1
$28 => 1
$29 => 1
$2A => 1
$2B => 1
$2C => 1
$2D => 1
$2E => 1
$2F => 1
$30 => 3
$31 => 2
$32 => 1
$33 => 1
$34 => 2
$35 => 2
$36 => 1
$37 => 1
$38 => 1
$39 => 1
$3A => 1
$3B => 1
$3C => 1
$3D => 1
$3E => 1
$3F => 1
$40 => 2
$41 => 2
$42 => 2
$43 => 3
$44 => 2
$45 => 2
$46 => 1
$47 => 1
$48 => 1
$49 => 1
$4A => 1
$4B => 1
$4C => 1
$4D => 1
$4E => 1
$4F => 1
$50 => 2
$51 => 2
$52 => 2
$53 => 3
$54 => 2
$55 => 2
$56 => 1
$57 => 1
$58 => 1
$59 => 1
$5A => 1
$5B => 1
$5C => 1
$5D => 1
$5E => 1
$5F => 1
$60 => 2
$61 => 2
$62 => 2
$63 => 3
$64 => 2
$65 => 2
$66 => 1
$67 => 1
$68 => 1
$69 => 1
$6A => 1
$6B => 1
$6C => 1
$6D => 1
$6E => 1
$6F => 1
$70 => 2
$71 => 2
$72 => 2
$73 => 1
$74 => 2
$75 => 3
$76 => 2
$77 => 2
$78 => 2
$79 => 2
$7A => 2
$7B => 2
$7C => 2
$7D => 2
$7E => 2
$7F => 2
$80 => 2
$81 => 2
$82 => 2
$83 => 1
$84 => 1
$85 => 3
$86 => 2
$87 => 2
$88 => 2
$89 => 2
$8A => 2
$8B => 2
$8C => 2
$8D => 2
$8E => 2
$8F => 2
$90 => 3
$91 => 2
$92 => 2
$93 => 1
$94 => 2
$95 => 2
$96 => 1
$97 => 1
$98 => 1
$99 => 1
$9A => 1
$9B => 1
$9C => 1
$9D => 1
$9E => 1
$9F => 1
$A0 => 2
$A1 => 2
$A2 => 2
$A3 => 1
$A4 => 1
$A5 => 0
$A6 => 2
$A7 => 2
$A8 => 2
$A9 => 2
$AA => 2
$AB => 2
$AC => 2
$AD => 2
$AE => 2
$AF => 2
$B0 => 2
$B1 => 2
$B2 => 2
$B3 => 1
$B4 => 3
$B5 => 3
$B6 => 3
$B7 => 3
$B8 => 3
$B9 => 3
$BA => 3
$BB => 3
$BC => 3
$BD => 3
$BE => 3
$BF => 3
$C0 => 2
$C1 => 2
$C2 => 2
$C3 => 1
$C4 => 1
$C5 => 2
$C6 => 1
$C7 => 1
$C8 => 1
$C9 => 1
$CA => 1
$CB => 1
$CC => 1
$CD => 1
$CE => 1
$CF => 1
$D0 => 2
$D1 => 2
$D2 => 2
$D3 => 1
$D4 => 1
$D5 => 3
$D6 => 1
$D7 => 1
$D8 => 2
$D9 => 2
$DA => 2
$DB => 2
$DC => 2
$DD => 2
$DE => 2
$DF => 2
$E0 => 1
$E1 => 2
$E2 => 1
$E3 => 1
$E4 => 1
$E5 => 2
$E6 => 1
$E7 => 1
$E8 => 1
$E9 => 1
$EA => 1
$EB => 1
$EC => 1
$ED => 1
$EE => 1
$EF => 1
$F0 => 1
$F1 => 2
$F2 => 1
$F3 => 1
$F4 => 1
$F5 => 2
$F6 => 1
$F7 => 1
$F8 => 1
$F9 => 1
$FA => 1
$FB => 1
$FC => 1
$FD => 1
$FE => 1
$FF => 1