Digital Electronics, Data Converters and Microprocessors — Practice

Question 1

Write -5 in 8-bit two's complement and state the range.

Accepted Answer

11111011. The range is -128 to +127.

Question 2

How many address lines does a 1K x 8 memory need?

Accepted Answer

Ten address lines, since 2^10 = 1024.

Question 3

How many flip-flops are needed for a mod-60 counter and for a Johnson counter of modulus 8?

Accepted Answer

A mod-60 counter needs 6 flip-flops (2^6 = 64). A Johnson counter of modulus 8 needs 4.

Question 4

A 4-bit DAC has a 5 V reference. Find the step size.

Accepted Answer

5/16 = 0.3125 V.

Question 5

Simplify F(A,B,C) equal to the sum of minterms 1, 3, 5 and 7.

Accepted Answer

The minterms are those where C = 1, so one group of four gives F = C.

Question 6

A register path has a propagation delay of 10 ns and a set-up time of 2 ns. Find the maximum clock frequency.

Accepted Answer

T is at least 12 ns, so fmax = 1/12 ns = about 83 MHz.

Question 7

How can a 4:1 multiplexer implement any three-variable function?

Accepted Answer

Use two variables as select lines and feed each data input with 0, 1, the third variable or its complement, read from the truth table.

Question 8

Name the five flags of the 8085.

Accepted Answer

Sign, zero, auxiliary carry, parity and carry.

Practice — Digital Electronics, Data Converters and Microprocessors