# Why Does My 19-bit Adder Using 74LS283 ICs Show Incorrect Results in Proteus?

• Comp Sci
• Lord Doppler
In summary, the problem is that the carry bit is getting through, but it's not being taken into account.
Lord Doppler
Homework Statement
Relevant Equations
Boolean Algebra, Logic
Hello, I'm doing a 19 bit adder in Proteus with the 74LS283 IC and I have a problem, I'm adding 1110111000110011010 (487834) with 0001110110001100111 (60519) which the result is 10000101111000000001 (548353) and Proteus doesn't the correct result. It is not taking into account the carry, someone can help me?

Why are you grounding S3 in the most significant digit? One should not ground any output, and you need that output to get your 20 bit result.

The carry bits seem to be getting through just fine.

Lord Doppler
Halc said:
Why are you grounding S3 in the most significant digit? One should not ground any output, and you need that output to get your 20 bit result.

The carry bits seem to be getting through just fine.
Because I need add 19 bits and not 20 bits I grounded S3 in the most significant digit, it's correct? I need add 19 bits and the carry

It is not correct to ground any output. You let it float if you don't care about the 20th bit. Grounding an output wastes energy at best, and burns out your chip at worst. I don't think LS technology will burn out since the fan-out implies an obvious current limit.

In that case, the 1st 19 bits of the the answer you got (shown in the bottom horizontal line) is correct. But you show 20 bits of answer, the last one being taken from the wrong line.

Lord Doppler said:
I need add 19 bits and the carry
The carry is the 21st bit. If you want 20 bits of output, s4 is that 20th bit, and it should be c4 that you let float. c4 is always going to be low anyway in the last chip.

I see you are calling the c4 line 's19', but it is actually 's20'. s19 is the s4 line, which you've grounded.

Last edited:
Lord Doppler
Halc said:
It is not correct to ground any output. You let it float if you don't care about the 20th bit. Grounding an output wastes energy at best, and burns out your chip at worst. I don't think LS technology will burn out since the fan-out implies an obvious current limit.

In that case, the 1st 19 bits of the the answer you got (shown in the bottom horizontal line) is correct. But you show 20 bits of answer, the last one being taken from the wrong line.

The carry is the 21st bit. If you want 20 bits of output, s4 is that 20th bit, and it should be c4 that you let float. c4 is always going to be low anyway in the last chip.

I see you are calling the c4 line 's19', but it is actually 's20'. s19 is the s4 line, which you've grounded.
Oh ok, then I will never ground an output, I didn't know. I tried float the C4 in the last chip and connect S4 to S19 for obtain the 20 bits in the output as you said and it works! Thanks

Halc

## 1. What is a 19-bit adder with 74LS283 ICs?

A 19-bit adder with 74LS283 ICs is a type of electronic circuit that is used to perform addition operations on binary numbers that have a length of 19 bits. It utilizes 74LS283 integrated circuits (ICs) which are commonly used in digital logic circuits.

## 2. How does a 19-bit adder with 74LS283 ICs work?

This type of adder works by taking in two 19-bit binary numbers and adding them together bit by bit. The 74LS283 ICs are responsible for performing the actual addition operations, while other components such as logic gates and flip-flops help control the flow of data and carry out the addition process.

## 3. What are the advantages of using a 19-bit adder with 74LS283 ICs?

One advantage is that it can handle larger binary numbers compared to traditional 8 or 16-bit adders. This makes it useful for applications that require more precision, such as in scientific calculations or data processing. Additionally, the 74LS283 ICs are readily available and relatively inexpensive, making this type of adder a cost-effective option.

## 4. Are there any limitations to using a 19-bit adder with 74LS283 ICs?

One limitation is that it can only perform addition operations and cannot handle other arithmetic operations such as subtraction or multiplication. Additionally, as the number of bits increases, the complexity of the circuit also increases, which can make it more prone to errors and require more power to operate.

## 5. How is a 19-bit adder with 74LS283 ICs different from other types of adders?

A 19-bit adder with 74LS283 ICs is different from other types of adders in terms of the number of bits it can handle and the specific ICs used in its design. Other types of adders, such as a ripple carry adder, may use different ICs and have different limitations and advantages. It is important to choose the right type of adder based on the specific needs of the application.

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