What is the difference of TTL and Logic

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wylee

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What is the voltage level difference of a TTL level and Logic level?

Say my voltage supply is 1.8V to GND
 

TTL logic levels are:
"1" > 2.4V
"0" < 0.4V
So if your device is driving by TTL it is almost OK. There is only 0.6V overdriving voltage. Usually it is acceptable for the most of CMOS devices. But if your device drives another TTL device it can has problem with logic "1" noise immunity.
 

just search for interfacing ttl and cmos. U'll find these in almost every digital electronics book.
 

TTL is one of the logic level standards. Besides TTL, we also have CMOS logic level. More details as follows:

TTL input thresholds
Vil (input low) is 0.8V max and Vih (input high) is 2.0V max. These thresholds are valid regardless of the supply voltage if the part is specified as "TTL level compatible"

TTL output levels
Vol (output low) is 0.4V max and Voh (output high) is 2.4V min. These are for an output loaded to its maximum specified load. At lighter loads, Vol will be lower (closer to 0.0) and Voh will be higher (closer to Vcc).
 

TTL is transistor transistor Logic
 

vcc voh vih vt vil vol
3.3TLL 3.3 2.4 2 1.5 0.8 0.4
5v TLL 5 2.4 2 1.5 0.8 0.4
5vCMOS 4 4.44 3.5 2.5 1.5 0.5
 

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