Why are digital systems more noise-immune than analog ones?

Only two levels must be distinguished, so small noise does not turn a 0 into a 1

Noise is added to the signal and later subtracted

How is a decimal digit coded in excess-3?

As the 4-bit binary of (digit + 3)

As the 4-bit binary of (digit - 3)

As the 4-bit binary of the digit itself

As the 7-bit ASCII value of the digit

What does self-complementing mean for excess-3?

Inverting the bits of a digit gives its 9's complement

Inverting the bits gives the 10's complement

Adding 1 gives the 9's complement

2079 Bhadra · 2+4 marks

Digital system advantages; BCD and Excess-3

Short answer

Digital systems provide noise immunity, easy storage, high accuracy, programmability, error detection, and high integration. BCD represents each decimal digit as 4-bit binary; excess-3 adds 3 to each digit before encoding, yielding a self-complementing code.

Write down the advantages of digital systems. Define BCD and excess-3 codes.

Advantages of digital systems

Noise immunity: small noise does not change 0 into 1, so results are reliable.
Easy storage: data is stored in memories without loss and copied exactly.
Accuracy and precision depend only on the number of bits, not on component drift.
Programmability: operation can be changed by software.
Error detection and correction using parity and codes.
Easy design and high integration: millions of gates on one IC give low cost, small size and low power.
Regeneration: signals can be restored by repeaters during transmission.

BCD code

BCD (8421) code represents each decimal digit 0–9 separately by its 4-bit binary value. Codes 1010–1111 are invalid. Example: $(59)_{10}$ = 0101 1001 (BCD).

Excess-3 code

Excess-3 (XS-3) is an unweighted BCD code in which each decimal digit is coded as the binary of (digit + 3). It is self-complementing: inverting the bits gives the 9's complement. Example: $(59)_{10}$ : 5 + 3 = 8 → 1000, 9 + 3 = 12 → 1100 → $(1000\ 1100)_{XS-3}$ .

Decimal	0	3	5	9
BCD	0000	0011	0101	1001
XS-3	0011	0110	1000	1100

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