What is the relationship between bytes and BCD codes

The BCD code is used to represent the decimal system in binary, and the BCD code is divided into compressed BCD code and uncompressed BCD code. A compressed BCD code is a byte representing two BCD codes, while an uncompressed BCD code is a byte representing an uncompressed BCD code.

Upstairs is good, e.g. a byte for a decimal number of 0 255, a byte for 0000 0000 1111 1111;The BCD code is a 4-digit binary number to represent the 10 digits of 0 9 in the 1-digit decimal number, commonly used is 8421-BCD code, each number has its own 8421 code: 0=0000 1=0001 2=0010 3=0011 4=0100 5=0101 6=0110 7=0111 8=1000 9=1001

A byte is 8 bits, and a BCD code is represented by a four-bit binary bit, so a byte can put two BCD codes.

Multiplication and division can be done without considering the base system, for example, the hexadecimal number 0ffh is stored in a, the decimal number 100 is placed in b, and then div ab, so a is equal to 02h, b is equal to 37h, and is equal to 55

In then suppose the number in a is ffh

binbcd:

mov b, 100 (b=100, decimal 100,).

div ab (a is equal to 02h, b is equal to 37h is equal to 55).

mov r3, a （a=02h）

mov a, #10 （a=10=0ah，b=55=37h）

xch a,b （a=55=37h, b=10=0ah)

div ab (a=05h=5 , b=5=05h)

swap a (a=50h,b=05h)

add a,b (a=55h,at this time, the bcd of the ten of you has been found,will.

37h = 55 converted to 55h

end1 What is the idea of solving this program?

The idea is to find the modulo and the to find a number to separate the hundreds, tens, and units.

For example 168168 100 = 1 surplus 68

68 10 = 6 and 8

8 1 = 8 remainder 0

In this way, hundreds, tens, and units are separated.

2 The second sentence of the program"div ab"The explanation is that the hexadecimal number is divided by 100, but the A should be stored in an eight-digit binary number, what is going on?

This is the way you don't understand the way the CPU stores data, the storage in a is actually a binary number in the final analysis, the machine only knows the binary number, after compiling this program, the decimal 100 we input also becomes a binary number, we usually say hexadecimal numbers because the hexadecimal number and the binary number have a bitwise correspondence, such as 1100 0110b=c6h That is to say, the binary number is written as a hexadecimal number every 4 digits and a paragraph, and the binary number is converted into hexadecimal number, 3 In the end, why add tens and single digits, isn't it necessary to separate tens and single digits?

I think if you know what the BCD code means, you will understand.

The BCD code is a hexadecimal number to represent the decimal number.

For example, 45h is equal to 69 in decimal, but if you say he is a bcd code, he represents the decimal number 45

Then you will find that not every hexadecimal number is BCD, for example AAH is not BCD, because there is no decimal number like AA.

I finally summarize, that is, what we call a decimal number or a hexadecimal number, in the final analysis, the machine is to turn it into a binary number, and the machine only knows the binary number, so that you can understand, we will not deal with the operation between different base numbers, and the operation must convert him to the same base number, the machine is also like this, but we are good at decimal operations, and the machine is good at binary operations, and the number of binary digits is inconvenient, so we found a helper hexadecimal number.

Hope you understand.

The following link has a detailed description of the BCD code, which is essentially unrelated, the BCD code is a way that the machine is using in processing, and the byte is a storage unit of memory.

Four. Such as:

Each byte is 8 bits and can store 8-bit BCD codes.