IC difference
- Thread starter bwaley
- Start date
74xx and 54xx series IC's are considered TTL, and generally need a Vcc of between 4.75 and 5.25v.
4000 series are CMOS, and can generally use a Vdd from 3v to 16v; some higher and lower than that.
The 74xx series generally consider a logic "0" to be anything below 0.8v.
A logic "1" is anything above around 2.8v.
CMOS will go from nearly Vss to Vdd on output swings.
There are Schmitt-trigger CMOS devices that see input voltages below 1/3 Vdd as a 0, and above 2/3 Vdd as a 1. The rest of them aren't so forgiving; slow rise times can cause high frequency oscillations and overheating.
CMOS device inputs must always have a path to Vdd or Vss. Letting them "float" is a recipie for disaster; they may oscillate at high frequency creating noise, or overheat due to operation in a linear mode.
4000 series are CMOS, and can generally use a Vdd from 3v to 16v; some higher and lower than that.
The 74xx series generally consider a logic "0" to be anything below 0.8v.
A logic "1" is anything above around 2.8v.
CMOS will go from nearly Vss to Vdd on output swings.
There are Schmitt-trigger CMOS devices that see input voltages below 1/3 Vdd as a 0, and above 2/3 Vdd as a 1. The rest of them aren't so forgiving; slow rise times can cause high frequency oscillations and overheating.
CMOS device inputs must always have a path to Vdd or Vss. Letting them "float" is a recipie for disaster; they may oscillate at high frequency creating noise, or overheat due to operation in a linear mode.
You can see the voltage levels of some logic families at this website
www.interfacebus.com/voltage_threshold.html
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