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Ever wonder what is a buffer and why is it useful? In this blog I will show you how to wire a 74ls240 TTL using NI Multisim and NI Ultiboard and some practical applications. First a few keywords:

Buffer = symbol is a triangle and its input is its output. Purpose is to slow current.

Octal = eight. The 74ls240 has eight inputs/outputs

Tri-state/3-state = allows an output port to assume a high impedance (Z) state in addition to low and high values.

Fan out= number of devices that an output is attached to.

A tri-state buffer or inverting buffer looks like a regular buffer or inverter, except there is an additional "enable" control signal entering the gate. When the enable is "1" the buffer is driving the output; when the enable is "0," the output is turned off ("tri-stated").

74ls04 vs 74ls240 Ok the 74ls04 takes its input and outputs the opposite i.e. high=low low=high. The 74ls240 is a bit more complex...kinda. It can also take its input and output the opposite depending on the G pin. This is what makes the 74ls240 different. The output is determined by pins G (1G or 2G) and pin 1A(1-4)/2A(1-4). When the G input is high, the output is "Z" and no electrical current flows through no matter if pins 1A(1-4)/2A(1-4) is high/low.

The 74LS240 belongs to 74XXYY IC series. The 74LS240 is a series of octal buffers and line drivers designed specifically to improve both the performance and density of three-state memory address drivers, clock drivers, and bus-oriented receivers and transmitters. The IC has a wide range of working voltage, a wide range of working conditions, and directly interfaces with CMOS, NMOS, and TTL. The output of the IC always comes in TTL which makes it easy to work with other TTL devices and microcontrollers. The IC 74LS240 is smaller in size and it has a much faster speed which makes it reliable in every kind of device.

Using NI Multisim I created a simply design to show how to use basic components to create an AND & OR gate.

Diode logic gates use diodes to perform OR and AND logic functions as shown in the circuit diagram. Connection of the LED at the output is optional which simply displays the logical state of the output, i.e. the logic state of output is 0 or 1, if LED is off or on, respectively.

Diodes have the property of easily passing an electrical current in one direction, but not the other. Thus, diodes can act as a logical switch. Diode logic gates are very simple and inexpensive, and can be used effectively in limited space.

However, they cannot be used extensively due to the obvious logic level shift when gates are connected

in series. In addition, they cannot perform a NOT function, so their usefulness is quite limited. This type of logic circuit is rarely found in integrated form.

OR Gate (74ls32)

If one or both inputs are at logic “1” (5 volts), the current will flow through one or both diodes. This current passes through the resistor and causes the appearance of a voltage across its terminals, thereby obtaining logic “1” on the output.

Here only a logic “0” (0 volts) on the output when both inputs are in logic “0”. In this case, the diodes do not conduct, there is no current through the resistor R and there is no voltage across its terminals. As a result the voltage at Vout is the same as ground (0 volts)

AND Gate (74ls08)

When both inputs are at logic “1″, the two diodes are reverse biased and there is no current flowing to ground. Therefore the output is logic “1” because there is no voltage drop across the resistor R.

If one of the inputs is logic “0”, the current will flow through the corresponding diode and through the resistor. Thus the diode anode (the output) will be logic “0”.

This method works fine when the circuits are simple, but there are problems when you have to make interconnections with such gates.

A while back I posted a blog about the 74ls163 Synchronous Counter. In this blog I will revisit the same TTL using Atanua software. After playing with the 73ls163 I gained a little more insight about it.

I found that (referring to the diagram) by changing the input values you can program the count up starting number. This TTL can only count up! To do this you will use input switches 1-4. Switch A is used to clear the counter and pin 2 is for clock connection. The "Ripple carry output" (RCO) used to enable successive cascaded stages. *floating pin in the diagram.

After setting your desired starting number, you can enable P, T & Load to start the count. You will see your project initiate from the programmed value. However, to keep the clock in a loop additional TTL's must be added; the 4 input Nand & Invertors. A nice project write up can be found here: synchronous-counters-163 Check out my YouTube video to see the simulation of 74ls163

In this blog, using the HP 50g, I will show you how to get to the built in equation library and solve equations for

straight wire magnetism. The units for such is Tesla.

If you are required to answer in Gauss you will need to convert.

After turning on your HP 50g:

Press APPS

Scroll down to #12 or type in 12 (Equation Library)

PressOK.IfSoft Menumode is on you will see four boxes.Eqlib Colib Mes Utils. Choose EQLIB. This is for the equation library.

In the library there are many choices. Today we will exploreMagnetism. Go ahead and scroll down, pressENTER.

This brings us to today's topic.Straight Wire. PressENTER. You should now see the see the equation. The soft key choices are now

Solv Equ Vars Pic -->Stk Exit

PIC will show you a visual of the straight wire equation.

Vars gives a description of each variable that can be used in the equation.

EQN is the equation itself. The --> Stk puts the equation onto the stack.

The main soft key choice is Solv. This is the equation solver. To enter numerical information you must first key in the constant ex: 5_cm radius and 4_A current; -press 5 then press F2Bthe key directly under thersoft key menu, then 4 and F4Dfor current...soft key menuI.

Now to solve for B we must first press the White Right Shift key <-- and then F5E(B soft key menu)

Then solver should output the answer. Play around with different equations to get a feel for the powerful HP 50g!

This is a simple 555 timer circuit however, it has been redesigned by Bits. My idea of circuits and TTL components should have a bit more color options and since they (colorful TTL's) don't exactly exist I thought I'd just give the world a taste of what future circuits could look like when future engineers take office!

I used Multisim software and Ultiboard to come up with this unique red color for the 555 Timer. Ultiboard allows the user to modify almost any component on the circuit. Another fantastic feature was the option to change the shape of the pcb board. No more boring rectangles! I have included some of the different shapes that were possible. Here's a quick video!

The 74181 is still used today in retro hacker projects. Here's ow it works and why it's so strange. Is it an all in one logic chip? Well, yes. Since it provides 16 Arithmetic Operations Add, Subtract, Compare, Double, Plus Twelve Other Arithmetic Operations as well as provides all 16 Logic Operations of Two Variables Exclusive — OR( XOR), Compare, AND, NAND, OR, NOR, Plus Ten other Logic Operations!

Why was it designed? To make computing faster in comparison with standard logic gates that was what available at the time. In March 1970, Texas Instruments introduced the 74181 Arithmetic / Logic Unit (ALU) chip, which put a full 4-bit ALU on one fast TTL chip. This chip provided 32 arithmetic and logic functions, as well as carry lookahead for high performance.

The SN54/74LS181 is a 4-bit Arithmetic Logic Unit (ALU) which can perform all the possible 16 logic, operations on two variables and a variety of arithmetic operations.

The 74181 ALU (arithmetic/logic unit) chip powered many of the minicomputers of the 1970s: it provided fast 4-bit arithmetic and logic functions, and could be combined to handle larger words, making it a key part of many CPUs.

The 74181 is a 4-bit slice arithmetic logic unit (ALU), implemented as a 7400 series TTL integrated circuit. The first complete ALU on a single chip,[1] it was used as the arithmetic/logic core in the CPUs of many historically significant minicomputers and other devices.

The 74181 represents an evolutionary step between the CPUs of the 1960s, which were constructed using discrete logic gates, and today's single-chip microprocessor CPUs. Although no longer used in commercial products, the 74181 is still referenced in computer organization textbooks and technical papers. It is also sometimes used in 'hands-on' college courses, to train future computer architects.

• Provides all 16 Logic Operations of Two Variables Exclusive — OR,

Compare, AND, NAND, OR, NOR, Plus Ten other Logic Operations

• Full Lookahead for High Speed Arithmetic Operation on Long Words

• Input Clamp Diodes

FUNCTIONAL DESCRIPTION

The SN54/74LS181 is a 4-bit high speed parallel Arithmetic Logic Unit (ALU). Controlled by the four Function Select Inputs (S0 . . . S3) and the Mode Control Input (M), it can perform all the 16 possible logic operations or 16 different arithmetic operations on active HIGH or active LOW operands. The Function Table lists these operations.

The combinational logic circuitry of the 74181 integrated circuit