1 Lecture #17 EGR 277 – Digital Logic Reading Assignment: Chapter 6 in Digital Design, 3 rd Edition by Mano Timing Sequences So far we have designed circuits to: produce desired outputs for certain input combinations (combinational circuits) produce a desired sequence of states or input output sequence (sequential circuits) One type of circuit that we have not directly dealt with is a circuit that will produce a series of control signals (or timing sequences) where each signal is HIGH or LOW for a specified length of time. Such timing sequences are often needed. Examples might include: signals to stop, start, and control the length of time for each cycle in a washing machine signals to control the RED, YELLOW, and GREEN signals for a stop light signals to control the opening and closing of valves

2 Lecture #17 EGR 277 – Digital Logic Example: Design a decoder to detect when count 4 occurs. Decoders – Can be used to indicate when certain counts occur. Similarly, they can be used to start or stop events at certain times. Example: Design a decoder to detect when counts 5, 7, or 15 occur. Also show how a 4x16 decoder could be used.

3 Lecture #17 EGR 277 – Digital Logic Example: Design a circuit that will output a signal that is HIGH for 3 seconds and LOW for 5 seconds.

4 Lecture #17 EGR 277 – Digital Logic Example: Design a circuit that will produce the following control signals.

5 Lecture #17 EGR 277 – Digital Logic Example: Design a traffic light controller with the following control signals. Notes: Whenever N/S Green or N/S Yellow are HIGH, E/W Red must also be HIGH. Whenever E/W Green or E/W Yellow are HIGH, N/S Red must also be HIGH. Handout: Traffic Light Controller schematic and PSPICE implementation Demo: Traffic Light Controller Circuit

6 Lecture #17 EGR 277 – Digital Logic Example: A register might be a group of 8 flip-flops used to store some binary data (byte or word). Sketch the circuit. Shift Registers Register - a group of binary storage cells (flip-flops) Common Register Uses: Temporary data storage and transfer Parallel-to-serial and serial-to-parallel conversion Data manipulation (complementation, rotation, etc) Shift register - A register is often also referred to as a "shift register" since one of its key functions involves the shifting of data through the register.

7 Lecture #17 EGR 277 – Digital Logic Example: A computer or microprocessor uses many types of registers, including CPU, PC, SP, ALU (with registers A and B), C, D, E, F (general purpose), I/O registers at ports, etc. Sketch. Also show some common assembly language instructions involving registers.

8 Lecture #17 EGR 277 – Digital Logic Common register functions: (briefly illustrate each) 1)Serial shifting of data (SISO - right or SISO - left) (SISO = Serial-input, Serial- output) 2)Parallel input of data (PI) 3)Parallel output of data (PO) 4)Rotation of data (left or right)

9 Lecture #17 EGR 277 – Digital Logic Parallel load shift register using D flip-flops - illustrate

10 Lecture #17 EGR 277 – Digital Logic Parallel load shift register with an enable Discuss the limitations of the prior shift register. Show how to implement the register above using SR or JK flip-flops and then add an enable (ANDed with each input).

11 Lecture #17 EGR 277 – Digital Logic Serial-In Serial-Out (SISO) register Illustrate using D flip-flops and JK flip-flops.

12 Lecture #17 EGR 277 – Digital Logic Rotation of data Illustrate rotate-right and rotate-left registers using D flip-flops and JK flip-flops.

13 Lecture #17 EGR 277 – Digital Logic Multi-function shift register Design a shift register with two mode controls, x and y, that will function as follows: xyFunction 00SISO - right 01Parallel load 10Rotate right 11Rotate left Show how to provide the input connections using logic gates or multiplexers Handout: 7495 Data Sheet. Discuss the features available on this 4-bit shift register.