What is 8421 BCD Code?

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The 8421 BCD code is one of the most commonly used binary codes in the field of digital electronics. This binary code is used to encode decimal digits from 0 to 9 in their equivalent binary format.

Read this chapter to learn all about 8421 BCD codes including its advantages, limitations, and applications.

What is 8421 BCD Code?

In digital electronics, the 8421 BCD code is a type of binary code. BCD stands for Binary Coded Decimal. The 8421 BCD code is the most widely used binary code for expressing decimal numbers in their equivalent binary format.

The 8421 BCD code is also known as the natural BCD code. It is a binary code used to represent each decimal digit by using a unique combination of 4-bits. It is a weighted binary code and is also a sequential binary code.

The digits 8421 represents the weights assigned to each of the four bits, where the most significant bit has a weight of 8 and the least significant bit has a weight of 1.

In the 8421 BCD code, each decimal digit can be represented by a unique 4-bit binary code. The following table highlights the 8421 BCD code for each decimal digit.

The 8421 BCD code is the most commonly used code in digital electronics to represent decimal numbers in binary form. It is mainly used in digital devices where human machine interface is required.

Advantages of 8421 BCD Code

In digital electronics, the 8421 BCD code has several advantages, mainly in applications where decimal numbers are used in a digital system. Some of the key benefits of the 8421 BCD code are given below −

• The 8421 BCD code provides a natural way of representing decimal numbers. This is because, we can directly encode each decimal digit into its equivalent 4-bit binary number.
• The 8421 BCD code allows for simple conversion between decimal and binary number systems. Hence, it is quite useful in digital devices where human input is required.
• The 8421 BCD code simplifies the arithmetic operations such as addition, subtraction, multiplication, and division of decimal numbers using a digital system like a calculator.
• The 8421 BCD code is compatible with decimal displays. Hence, it is commonly used in digital devices where the output has to be displayed on a decimal-based display like 7-segment display.

All these are the main advantages of 8421 BCD code. However, there are also some disadvantages of 8421 BCD code, lets discuss them.

Disadvantages of 8421 BCD Code

Listed below are some of the major disadvantages of using the 8421 BCD code −

• The 8421 BCD code is relatively less efficient than the pure binary code, as it requires a greater number of bits to represent a decimal number. For example, the decimal number 15 can be represented as 1111 in pure binary, whereas 0001 0101 in 8421 BCD.
• The arithmetic operations such as addition, subtraction, multiplication, and division performed in 8421 BCD code are relative more complex than they are in pure binary.
• The 8421 BCD code consumes more storage space as it uses 4 bits to represent each decimal digit.
• In the case of 8421 BCD code arithmetic, the rules of binary arithmetic cannot be applied to the entire 8421 BCD number, but only to the individual groups of 4-bits.
• The 8421 BCD codes are not suitable in applications where speed and efficiency are critical.
• In 8421 BCD code, there are six illegal code combinations. They are 1010, 1011, 1100, 1101, 1110, and 1111.

Thus, all these are the main disadvantages of the 8421 BCD code.

Applications of 8421 BCD Code

The 8421 BCD code is widely used in various applications in digital electronics. Given below are some of the key applications of the 8421 BCD code −

The 8421 BCD code is mainly used in digital displays used in calculators, digital clocks and watches, etc. where decimal digits are to be displayed.

• The 8421 BCD code is also used in device that accept numeric inputs like calculators.
• In process control systems, the 8421 BCD code is used to represent and manipulate the decimal values.
• The 8421 BCD codes are also used in embedded systems where human machine interaction is critical.
• The 8421 BCD code is widely used in control panels of various electronic devices to display numerical values.

This is all about the basics of the 8421 BCD code. In the next section, we will explain how you can perform addition and subtraction of 8421 BCD codes.

Addition in 8421 BCD Code

The addition operations in 8421 BCD code are performed by individually adding the corresponding digits of the given decimal numbers expressed in 4-bit binary form.

In BCD addition, if there is no end-around carry, the sum is not an illegal BCD code. Thus, it does not require any correction.

If there is an end-around carry from one group to the next group, of if the sum is an illegal code, then it is corrected by adding 0110 to the sum term and the resulting carry is added to the next group.

Let us understand the BCD addition with the help of an example.

Example

Add 251 and 353 in the 8421 BCD code.

Solution

Converting the given decimal numbers into BCD code,

251 = 0010 0101 0001

353 = 0011 0101 0011

Adding the BCD codes,

Hence, the sum of 251 and 353 is 604.

Subtraction in 8421 BCD Code

To perform subtraction of decimal numbers using 8421 BCD code, we first convert the given decimal numbers into their 8421 BCD codes. Then, we subtract the BCD subtrahend from the BCD minuend starting from the LSD.

If there is no borrow from the next higher group, then no correction is needed. If there is a borrow from the next higher group, then the result has to be obtained by subtracting 0110 from the intermediate difference term.

Let us take an example to understand the BCD subtraction.

Example

Subtract 15 from 25 in 8421 BCD code.

Solution

Converting the given decimal number into BCD code,

25 = 0010 0101

15 = 0001 0101

Subtracting the BCD code,

Hence, the difference of 25 and 15 is 10.

Conclusion

In conclusion, the 8421 BCD code is a natural binary coded decimal code widely used in digital electronics. It is primarily used in applications where decimal digits and human interaction are critical.

The most significant advantage of the 8421 BCD code is that it provides an easy conversion to and from decimal numbers. But it is less space efficient code because it requires more bits to represent a decimal digit.