aaa和daa指令是什么意思，我看了半天都看不懂，它们和BCD有什么关系？

2002-04-29 11:13:17 1.5k 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

新手避坑指南：PCF85063 RTC芯片BCD码转换与时间设置实战（附代码）本文详细介绍了PCF85063 RTC芯片的开发实战，包括BCD码转换、时间寄存器配置及常见问题排查。通过实际案例和代码示例，帮助开发者避免常见陷阱，提升RTC芯片的使用效率和精度。阅读详情

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双Windows 10启动菜单名称修改全攻略：bcdedit与工具实操从操作系统引导机制说起，Windows启动管理器依赖BCD（启动配置数据）存储每个系统的显示名称与GUID。多重系统环境下，默认的“Windows 10”条目容易混淆，这涉及UEFI与Legacy不同引导方式下BCD的存储位置差异。理解bcdedit /set命令可精准重命名启动项，并配合备份与恢复技巧保障安全。该技术广泛用于双系统管理、系统维护与PC重装场景，帮助用户快速识别工作与娱乐系统，避免进错环境。本文基于实际排查经验，给出命令行与图形化工具（BootICE、EasyBCD）的完整操作方案，解决菜单阅读详情

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切换为时间正序

sandwish2000 2002-04-30

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是加法的bcd调整命令.
aaa
1 如果al中的低4位在0-9之间,且af为0,则转3
2 如果al中的低4位在a-f之间或af为1,则al=(al)+6;ah=(ah)+1;af=1
3 清除al的高4位
4 af的值送cf位
daa
1 如果al的低4位在a-f之间或af为1,则al=(al)+6,af=1
2 如果al中的低4位在a-f之间或cf为1,则al=(al)+60h,cf=1

awinder 2002-04-29

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AAA - Ascii Adjust for Addition
37 AAA ASCII adjust AL after addition

Description
Adjusts the sum of two unpacked BCD values to create an unpacked BCD result. The AL register is the implied source and destination operand for this instruction. The AAA instruction is only useful when it follows an ADD instruction that adds (binary addition) two unpacked BCD values and stores a byte result in the AL register. The AAA instruction then adjusts the contents of the AL register to contain the correct 1-digit unpacked BCD result.

If the addition produces a decimal carry, the AH register is incremented by 1, and the CF and AF flags are set. If there was no decimal carry, the CF and AF flags are cleared and the AH register is unchanged. In either case, bits 4 through 7 of the AL register are cleared to 0.

Operands Bytes Clocks
1 3 NP

Flags
The AF and CF flags are set to 1 if the adjustment results in a decimal carry; otherwise they are cleared to 0. The OF, SF, ZF, and PF flags are undefined.

AAD - Ascii Adjust AX Before Division
D5 0A AAD ASCII adjust AX before division
D5 ib (No mnemonic) Adjust AX before division to number base imm8

Description
Adjusts two unpacked BCD digits (the least-significant digit in the AL register and the most-significant digit in the AH register) so that a division operation performed on the result will yield a correct unpacked BCD value. The AAD instruction is only useful when it precedes a DIV instruction that divides (binary division) the adjusted value in the AX register by an unpacked BCD value.

The AAD instruction sets the value in the AL register to (AL + (10 * AH)), and then clears the AH register to 00H. The value in the AX register is then equal to the binary equivalent of the original unpacked two-digit (base 10) number in registers AH and AL.

The generalized version of this instruction allows adjustment of two unpacked digits of any number base (see the "Operation" section below), by setting the imm8 byte to the selected number base (for example, 08H for octal, 0AH for decimal, or 0CH for base 12 numbers). The AAD mnemonic is interpreted by all assemblers to mean adjust ASCII (base 10) values. To adjust values in another number base, the instruction must be hand coded in machine code (D5 imm8).

Operands Bytes Clocks
2 10 NP

Flags
The SF, ZF, and PF flags are set according to the result; the OF, AF, and CF flags are undefined.

Lesily 2002-04-29

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ASCII 码的加法调整 AAA

用途：AAA指令用于对两个未压缩的十进制数相加而在AL中产生的一个未压缩的十进制结果进行校正。
格式：AAA(不带操作数)
例子：AAA；after the addition

ASCII 码的除法调整 AAD

用途：在一条指令对两个未压缩的十进制操作进行除法运算之前，AAD对AL中的被除数进行调整，以便除法的结果将是一个未压缩的十进制的商。
格式：AAD(不带操作数)
例子：AAD；prior to the division

aaa和daa指令是什么意思，我看了半天都看不懂，它们和BCD有什么关系？

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