Multisim and Ultiboard| 74ls240 wired 3D PCB

74ls240 Wired

Written by Larsha Johnson

8/20/2015

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.