14. Can you think of different ways to construct a digital memory element beginning with ’’opposite’’ terms such as on-off , in-out, up-down, right-left, cold-hot, wet-dry, etc.?
15. What logic level will appear at A if the flip-flop in in Fig. 1-16 has SET =L and RESET= H?
16. Look at the binary representation of the decimal number 9 in Table 1-1 How many bits are there in this binary number? If it is stored in the register in Fig. 1-17, what are the bit values of DCBA?
17. If a shift operation requires a time of 1us to complete, how long would it take to enter an 8-bit number into the parallel register in Fig. 1-18a? How long would it take to enter an 8-bit number into the serial register in Fig. 1-18b?
18. When we speak of a microprocessor, what is meant by the term port?
1-5DIGITAL POERATIONS
COUNTERS
It was mentioned previously that counting is an operation easily performed by a digital circuit. A digital circuit designed to keep track of a number events, or to count, is called a counter. The counter in Fig. 1-21a is constructed using a number of flip-flops (n) and additional electronic circuit. It is similar to a storage register, since it is capable of storing a binary number. The input to this counter is the rectangular waveform labeled clock. Each time the clock signal changes state from low to high, the count will add one (1) to the number stored n its flip-flops. In other words, this counter will the number of
Fig 1-21 (a) A counter constructed with n flip-flops. (b) A count of 6.