High Leading edge Low Trailing edge Positive logic pulse Negative logic pulse Trailing edge High Leading edge Low Pulse width  Pulse characteristic from a databus  Rise  time  50% 5 V  Pulse  amplitude  (10 volts)  90% 9 V  10% 1 V  Fall  time  A  X  X  X  B  A  B  A  B  C  C  D  Input = 1  (High)  Output = 0  (Low)  Input  Output  High  Low  Low  High  Figure 12-255.  AND gate logic symbol.  Figure 12-252.  Non-ideal pulse and its characteristics.  Figure 12-254.  Possible logic states.  Figure 12-253.  Standard logic symbol.  Figure 12-251.  Positive and negative pulse in an idealized form.  The Inverter Logic  The AND Gate  Basic Logic Circuits  12-123  Boolean logic is a symbolic system used in representing the  truth value of statements. It is employed in the binary system  used by digital computers primarily because the only truth  values (true and false) can be represented by the binary digits  1 and 0. A circuit in computer memory can be open or closed,  depending on the value assigned to it. The fundamental  operations of Boolean logic, often called Boolean operators,  are “and,” “or,” and “not;” combinations of these make up 13  other Boolean operators. Six of these operators are discussed.  be assumed as instantaneous.  Figure 12-252  shows the non- ideal pulse and its characteristics. The time required for a  pulse to go from a low state to a high state is called the rise  time, and the time required for the pulse to return to zero is  called the fall time. It is common practice to measure the rise  and fall time between 10 percent amplitude and 90 percent  amplitude. The reason for taking the measurements in these  points is due to the non-linear shape of the pulse in the first  10 percent and final 90 percent of the rise and fall amplitudes.  The pulse width is defined as the duration of the pulse. To be  more specific, it is the time between the 50 percent amplitude  point on both the pulse rise and fall.  The AND gate is made up of two or more inputs and a single  output. The logic symbol is shown in  Figure 12-255 . Inputs  are on the left and the output is on the right in each of the  The inverter circuit performs a basic logic function called  inversion. The purpose of the inverter is to convert one logic  state into the opposite state. In terms of a binary digit, this  would be like converting a 1 to a 0 or a 0 to a 1. When a  high voltage is applied to the inverter input, low voltage is  the output. When a low voltage is applied to the input, a high  voltage is on the output. This operation can be put into what  is known as a logic or truth table. The standard logic symbol  is shown in  Figure 12-253 .  Figure 12-254  shows the possible  logic states for this gate. This is the common symbol for an  amplifier with a small circle on the output. This type of logic  can also be considered a NOT gate. 