The 74HC; 74HCT has octal non-inverting buffer/line drivers with 3-state Ci input capacitance. -. -. pF. CPD power dissipation. The SNx4HC octal buffers and line drivers are designed specifically to improve both the performance and density of 3-state memory address drivers, clock. I need a logic buffer for 8-bit microcontroller port, like 74HC, but with an output current of more than 20mA, to drive high current LED.
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Many different symbols can be used to represent each of these eight basic logic gate elements. Two useful variations of these American symbols are also widely used and are shown added to a standard inverter symbol in Figure 2 ; the left-hand symbol is internationally recognized and indicates that the logic element has a Schmitt trigger input action; the right-hand symbol — which is widely used but is not universally recognized — indicates that the logic element has an open-drain o.
The functional action of any logic gate can be described either in words or in a tabular or symbolic way. The following list describes the functions of all eight basic types of logic gates in words.
Figure 3 shows how the functions of the eight basic types of gates can also be presented in tabular form via truth tables which show the logic state of the output at all possible input logic state combinations or symbolically via Boolean algebraic terms.
Note that, by convention, all logic gate inputs are notated alphabetically as A, B, C, etc. Also note in the Boolean expressions that a negated output is indicated by a negation bar drawn above the basic output symbol; the negated state is called a not state; thus, a negated Y output is called a not-Y output. All modern digital logic circuitry assumes the use of the positive logic convention, in which a logic 1 state is high and a logic 0 state is low. With this point in mind, Figure 4 presents a basic set of two-input positive and negative logic equivalents.
Thus, it can be seen that a negative logic AND gate action — in which the output is low only when both inputs are low — is directly 74hc44 from a positive logic OR gate, and so on.
Digital buffer ICs have two main purposes: If you ever need only a few simple buffers, one cheap way to get them is to make them from spare AND or OR elements as shown in Figure 5 or from pairs of normal or Schmitt inverters as shown in Figure 6. Figure 7 lists basic details of nine popular, non-inverting digital buffer ICs. In CMOS devices, the unused inputs can be tied directly to either supply line, but jc TTL devices, it is best for lowest quiescent current consumption to tie all unused inputs high via a common 10K resistor.
If the unused buffer is a three-state type, it should if it has independent control be set into its normal mode via its control input. Dealing now with the individual buffer ICs listed in Figure 7Figure 8 shows the functional diagram and truth table, etc. Thus, any unwanted elements should be disabled by tying their C terminals low and their A terminals high, using one of the methods shown in Figure 9. Any element can be used as a normal buffer by grounding its C terminal Figure 10or as a three-state buffer that drives a common bus line by using it as shown in Figure Thus, this IC can be used as a simple Hex buffer by wiring 74hc244 as shown in Figure 14 with pins 1 and 15 groundedor as a Hex three-state buffer that is controlled via a single input by wiring it as shown in Figure 15 with pins 1 and 15 shorted together and used as a DISABLE input.
Figure 16 shows the functional 74uc244 of thewhich is a standard TTL Hex buffer in which each buffer has an i output that can sink up to 40 mA and can be connected to a supply of up to 30V via an external current-limiting pull-up resistor but the actual IC must use a 5V supply.
Figure 17 shows how one of these buffers can be used as a 5V to high-voltage up to 30V non-inverting interface. Figure 18 shows how three o. The circuit action is such that the output is pulled low when any input is 74hv244, and only goes high when all three inputs are high, thus giving an AND action. Figure 19 shows the functional diagram and basic truth table of a 74LS Hex three-state buffer IC, in which all six buffers share a common AND-gated control line. Uc IC can be used as six normal buffers by grounding its two control pins as shown in Figure 20or as a set of six three-state buffers that are all switched via one common control signal as shown 74h244 Figure 21 ; AND-type three-state control can be obtained by using both Control terminals pins 1 and The IC is really a dual Quad device, ci which buffers are controlled via the CA terminal, and buffers are controlled via the CB terminals.
Each of these Quads can be used as a set of simple Schmitt buffers by grounding its control terminal as shown in Figure 23 aor as a ganged set of three-state Schmitt buffers by using its control terminal as shown in Figure 23 b. Need to brush up on your electronics principles? These multi-part series may be just what you need! Part 4 Practical digital mixed gate and special-purpose logic gate ICs such as programmable logic, majority logic, and digital transmission gate types.
Learning Electronics Need to brush up ci your electronics principles?
IC 74HC | Nano Elektronika, d.o.o.
Symbols, truth tables, and Boolean expressions for the eight basic types of logic gates. Basic sets of two-input positive and negative logic equivalents. Any two elements from an inverter IC can be used to make a non-inverting buffer element. Nine popular non-inverting buffer ICs. Functional diagram and truth table, etc.
All unwanted 74hc424 elements must be connected in one of these ways. Methods of using a 74LS element as a normal buffer. Methods of using a 74LS element as a three-state line-driving buffer. Functional diagram and truth table of the B Hex buffer IC. Method of connecting the B for use as six normal buffers. Method of connecting the B for use as a three-state Hex buffer controlled via a single input.
Functional diagram of the Hex buffer with 30V o. Three buffers used to make a three-input wired AND gate. Functional diagram and truth table of the 74LS Hex three-state buffer.
Methods of connecting the 74LS for use as six normal buffers. Methods of connecting the 74LS for use as a three-state Hex buffer controlled via a single input. The 74LS Quad buffers can be used as a simple Schmitt buffers, or as b three-state ganged Schmitt buffers.