Multisim and Ultiboard| 74ls240 wired 3D PCB

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.


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