HPK taruh disini
Logic symbols are used to represent the logic functions in a more
abstract way, allowing the designer to specify the logical function of a
circuit without getting into the details of the underlying components
(such as the transistors and resistors). The logic symbols used in this
text represent those that are most commonly used in commercial
documentation.
There are other standards, such as the ANSI/IEEE standard gate level symbols, but they are not encountered as frequently in practice. Figure bellow shows the logic symbols for different gates, and their functions are described in the truth tables.
The logic symbols in figure above show the shapes and Boolean logic functions for the most common gate configurations. The buffer device is a triangle--the symbol for an amplifier because it amplifies the input signal, allowing an increase in the number of loads that can be driven. Note that a small circle, often referred to as a "bubble," on an input or output terminal designates a logical inversion. Thus the inverter is shown as a triangle (amplifier) with a bubble on the output to signify the logic level inversion on the output. The logic voltage levels for TTL logic are:
Positive Logic
0 = false - lowest voltage level
0 - input voltages 0 to 0.8 volts (low)
1 - input voltages 2 to 5 volts (high)
This means that a TTL compatible logic input is guaranteed to respond to an input signal between 0 and 0.8 volts as a logic zero, and input voltages from 2 to 5 volts as a logic one. Note that voltages between 0.8 and 2 volts are not valid logic levels.
Logic voltage levels are different for different types of logic, but the most common logic levels are those corresponding to the original TTL (transistor-transistor logic), using a 5 volt power supply CMOS levels, using 3 or 5 volt power, are also common. TTL and CMOS logic--like almost every other type of logic in common use--are called positive logic because the most positive voltage corresponds to the logic one value.
There are other standards, such as the ANSI/IEEE standard gate level symbols, but they are not encountered as frequently in practice. Figure bellow shows the logic symbols for different gates, and their functions are described in the truth tables.
The logic symbols in figure above show the shapes and Boolean logic functions for the most common gate configurations. The buffer device is a triangle--the symbol for an amplifier because it amplifies the input signal, allowing an increase in the number of loads that can be driven. Note that a small circle, often referred to as a "bubble," on an input or output terminal designates a logical inversion. Thus the inverter is shown as a triangle (amplifier) with a bubble on the output to signify the logic level inversion on the output. The logic voltage levels for TTL logic are:
Positive Logic
0 = false - lowest voltage level
1 = true = highest voltage level
Corresponding TTL Logic Voltages0 - input voltages 0 to 0.8 volts (low)
1 - input voltages 2 to 5 volts (high)
This means that a TTL compatible logic input is guaranteed to respond to an input signal between 0 and 0.8 volts as a logic zero, and input voltages from 2 to 5 volts as a logic one. Note that voltages between 0.8 and 2 volts are not valid logic levels.
Logic voltage levels are different for different types of logic, but the most common logic levels are those corresponding to the original TTL (transistor-transistor logic), using a 5 volt power supply CMOS levels, using 3 or 5 volt power, are also common. TTL and CMOS logic--like almost every other type of logic in common use--are called positive logic because the most positive voltage corresponds to the logic one value.
