What is a non combined BCD code and what is a combined BCD code?

Each byte of internal memory is made up of eight-bit binary numbers, and BCD code is made up of four-bit binary numbers. If the octe-bit byte stores a BCD code, it is called a non-combined BCD code, the upper four bits are 0, and the lower four bits store a BCD code; If two BCD codes are stored in one byte in the octaves, it is called a combined BCD code, the upper four bits store one BCD code 1, and the lower four bits store another BCD code 2.

A four-digit binary number is used to represent a decimal number, and this encoding is called a BCD code (also called 8421 code), which is a decimal number represented by a binary number.

Decimal digits.

BCD code. Example 1: Convert the decimal number 9207 to BCD code.

Solution: The BCD code of 7209 is: 0111001000001001

Exercise: Find the BCD code for the decimal number 4851.

2. A few notes on the BCD code:

1) Considering people's usage habits, the decimal system is usually used in the process of computer input and output, and then converted into binary by the machine. The form of the BCD code is very suitable for this habit of human beings.

2) Although the BCD code also uses a four-digit binary number encoding to represent each decimal number, it does not convert the value of the decimal number into a real binary value, and cannot be evaluated according to the weight.

For example, the decimal number 28 is converted to binary: 11100

The decimal number 28 is converted to BCD code as: 00101000

Therefore, the conversion between the BCD code and the binary system cannot be carried out directly, it must be converted into decimal system first, and then converted to binary, because the BCD code is essentially a decimal number, and the form is a binary number, and the conversion is similar to the conversion between binary numbers and hexadecimal numbers. Therefore, when studying, be careful not to confuse and distinguish between them.

There are two formats that are often used for BCD codes in computers, namely detached BCD codes and combined BCD codes.

The so-called split BCD code is to use a one-byte lower four-digit encoding to represent a digit of a decimal number, for example, the number 82 is stored in the format:

1 0 0 0 0 0 1 0 where represents an irrelevant value.

The combination of BCD code is to store a two-digit decimal number in a byte, and the storage format of example 82 is 1000 0010

Use a 4-digit binary number to represent the 10 digits 0 9 in a 1-digit decimal number, referred to as BCD code, that is, BCD**. Binary-coded decimal (abbreviated as BCD), known as BCD code or binary decimal **, also known as binary decimal number. It is a form of binary numeric encoding, with binary encoded decimal**.

Non-BCD code is an encoding other than BCD code, such as a hexadecimal code.

BCD code, it is a decimal number represented in binary, this method is to use a combination of 4-digit binary code to represent the decimal number of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ten digits. There are 16 combinations of 4-digit binary numbers, and in principle, you can choose 10 of them as **, which represent the ten symbols of 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 in the decimal system. The most commonly used BCD code is called 8421BCD code, which is a 4-digit binary digit value.

In the 8421BCD code, **1010 1111 is not used, which is called a fake code.

The compressed BCD code is represented by 4-bit binary, 1 byte (8-bit binary) represents the 2-bit BCD code, such as 10010011b represents the decimal number 93 The uncompressed BCD code is represented by 1 byte, the upper 4 bits are always 0000, remember always, the lower 4 bits are represented by 0000--1001 means 0--9, such as 93 is represented by 0000100100000011, accounting for 2 bytes, and the 00001001 represents 9,00000011 means 3

The BCD code is a one-to-one correspondence, e.g., 123 in decimal is expressed by BCD as: 0001 0010 0011 because:

The decimal 1 is 0001 in binary 2 in binary is 0010 in decimal 3 is 0011 in binary The difference from binary: The binary of 123 should be obtained by short division 1111011 It can be seen that the BCD code is only mechanically binary to represent each bit of the decimal. Compressed vs. uncompressed:

Since 1 byte has 8 bits (8 0s or 1s), if you use one byte to store 4 bits of BCD code (the rest of which are filled with 0), it is uncompressed, such as 123:00000001 00000010 0011 in decimal, and if you use one byte to store 8 bits of BCD code, it is compressed, such as 123:0001 0010 0011 in decimal