Chapter 3 (part 2) Basic Logic Gates 1

3-7 The Inverter Used to complement (invert) a digital signal When A = 1, X = 0 When A = 0, X = 1 Timing analysis

Truth table and Boolean equations for the Inverter X = A Inversion bar Used to signify the complement Inverter is also called as NOT gate Truth Table

3-8 The NAND Gate Same as the AND gate except that its output is inverted If A = 1 and B = 1, X = 0 If A = 0 or B = 0, A = 1

I/O of a 7400 quad NAND IC

Truth table and Boolean equations for the NAND Gate Boolean Equation: X = AB Multiple inputs - the output is always HIGH unless all inputs go HIGH

Symbols for three- and eight-input NAND gates

3-9 The NOR Gate Same as the OR gate except that its output is inverted If A = 1 or B = 1, X = 0 If A = 0 and B = 0, X = 1

I/O of a 7402 quad NOR IC

Truth Table and Boolean equation for The NOR Gate Boolean Equation: X = A + B

3-10 Logic Gate Waveform Generation A popular general Purpose Repetitive waveform generator To create specialized waveforms, we use Basic gates, and a clock oscillator, and A repetitive waveform generator circuit

Figure 3.44 Generating a 3-ms HIGH pulse using an AND gate and a Johnson shift counter.

Example 3-13 Which Johnson counter outputs will you connect to an AND gate to get a 1ms HIGH-level output from 4 to 5ms?

Example 3-14 Which Johnson counter outputs must be connect to a three-input AND gate to enable just the Cp#4 pulse only to be output?

Example 3-15 Sketch the output waveform resulting from inputting the Johnson counter outputs shown:

Figure 3.60 7404 TTL and 4049 CMOS inverter pin configurations.

Figure 3.61 (a) 7402 TTL NOR and 4001 CMOS NOR pin configurations; (b) 7400 TTL NAND and 4011 CMOS NAND pin configurations.

3-12 IEEE/IEC Standard Logic Symbols

Summary The AND gate requires that all inputs are HIGH in order to get a HIGH output. The OR gate outputs a HIGH if any of its inputs are HIGH. An effective way to measure the precise timing relationships of digital waveforms is with an oscilloscope or a logic analyzer.

Summary Beside providing the basic logic functions, AND and OR gates can also be used to enable or disable a signal to pass from one point to another. There are several integrated circuits available in both TTL and CMOS that provide the basic logic functions.

Summary Two important troubleshooting tools are the logic pulser and the logic probe. The pulser is used to inject pulses into a circuit under test. The probe reads the level at a point in a circuit to determine is it is HIGH, LOW, or floating. An inverter provides an output that is the complement of its input.

Summary A NAND gate outputs a LOW when all of its inputs are HIGH. A NOR gate outputs a HIGH when all of its inputs are LOW. Specialized waveforms can be created by using a repetitive waveform generator and the basic gates. 40