Month: January 2020
-
12.5 Universal Shift Registers: Parallel-in, Parallel-out
The purpose of the parallel-in/ parallel-out shift register is to take in parallel data, shift it, then output it as shown below. A universal shift register is a do-everything device in addition to the parallel-in/ parallel-out function. Above we apply four bit of data to a parallel-in/ parallel-out shift register at DA DB DC DD.…
-
12.4 Shift Registers: Serial-in, Parallel-out (SIPO) Conversion
A serial-in, parallel-out shift register is similar to the serial-in, serial-out shift register in that it shifts data into internal storage elements and shifts data out at the serial-out, data-out, pin. It is different in that it makes all the internal stages available as outputs. Therefore, a serial-in, parallel-out shift register converts data from serial…
-
12.3 Shift Registers: Parallel-in, Serial-out (PISO) Conversion
Parallel-in/ serial-out shift registers do everything that the previous serial-in/ serial-out shift registers do plus input data to all stages simultaneously. The parallel-in/ serial-out shift register stores data, shifts it on a clock by clock basis, and delays it by the number of stages times the clock period. In addition, parallel-in/ serial-out really means that…
-
12.2 Shift Registers: Serial-in, Serial-out
Serial-in, serial-out shift registers delay data by one clock time for each stage. They will store a bit of data for each register. A serial-in, serial-out shift register may be one to 64 bits in length, longer if registers or packages are cascaded. Below is a single stage shift register receiving data which is not…
-
12.1 Introduction to Shift Registers
Shift registers, like counters, are a form of sequential logic. Sequential logic, unlike combinational logic is not only affected by the present inputs, but also, by the prior history. In other words, sequential logic remembers past events. Shift registers produce a discrete delay of a digital signal or waveform. A waveform synchronized to a clock,…
-
11.5 Finite State Machines
Up to now, every circuit that was presented was a combinatorial circuit. That means that its output is dependent only by its current inputs. Previous inputs for that type of circuits have no effect on the output. However, there are many applications where there is a need for our circuits to have “memory”; to remember…
-
11.3 Synchronous Counters
What is a Synchronous Counter? A synchronous counter, in contrast to an asynchronous counter, is one whose output bits change state simultaneously, with no ripple. The only way we can build such a counter circuit from J-K flip-flops is to connect all the clock inputs together, so that each and every flip-flop receives the exact…
-
11.2 Asynchronous Counters
In the previous section, we saw a circuit using one J-K flip-flop that counted backward in a two-bit binary sequence, from 11 to 10 to 01 to 00. Since it would be desirable to have a circuit that could count forward and not just backward, it would be worthwhile to examine a forward count sequence…
-
11.1 Binary Count Sequence
If we examine a four-bit binary count sequence from 0000 to 1111, a definite pattern will be evident in the “oscillations” of the bits between 0 and 1: Note how the least significant bit (LSB) toggles between 0 and 1 for every step in the count sequence, while each succeeding bit toggles at one-half the…
-
10.8 Monostable Multivibrators
We’ve already seen one example of a monostable multivibrator in use: the pulse detector used within the circuitry of flip-flops, to enable the latch portion for a brief time when the clock input signal transitions from either low to high or high to low. The pulse detector is classified as a monostable multivibrator because it…
-
10.7 Asynchronous Flip-Flop Inputs
The normal data inputs to a flip flop (D, S and R, or J and K) are referred to as synchronous inputs because they have effect on the outputs (Q and not-Q) only in step, or in sync, with the clock signal transitions. These extra inputs that I now bring to your attention are called…
-
10.6 The J-K Flip-Flop
Another variation on a theme of bistable multivibrators is the J-K flip-flop. Essentially, this is a modified version of an S-R flip-flop with no “invalid” or “illegal” output state. Look closely at the following diagram to see how this is accomplished: The J and K Inputs What used to be the S and R inputs…
-
10.5 Edge-triggered Latches: Flip-Flops
So far, we’ve studied both S-R and D latch circuits with enable inputs. The latch responds to the data inputs (S-R or D) only when the enable input is activated. In many digital applications, however, it is desirable to limit the responsiveness of a latch circuit to a very short period of time instead of…
-
10.4 The D Latch
Since the enable input on a gated S-R latch provides a way to latch the Q and not-Q outputs without regard to the status of S or R, we can eliminate one of those inputs to create a multivibrator latch circuit with no “illegal” input states. Such a circuit is called a D latch, and…