CMOS IC with TTL I/O levels

[myatham]

Hi,
What is the difference between CMOS IC and TTL IC? I found in one CMOS IC datasheet that it logic levels are LVTTL levels?
How TTL levels are achived with CMOS IC? CMOS IC means it will have CMOS logic levls only. Please correct me if i am asssuming wrong and help me to get rid of this confusion...


Thanks,
Mallikarjun Y

 

[ymhatre]

Use optocouplers to acheive the required ttl levels from cmos for level conversion

 

[kandhu26]

AT89C51, Where 'C' implies CMOS +5V with +or- 0.25 tolerance [4.75V to 5.25V]
AT89S51, Where 'S' implies Reduced voltage +V with +or- 0.5V tolerance [4.5V to 5.5V]
AT89LV51, Where 'LV' implies Low voltage +3.3V
74LS00, Where 'LS' implies Low power Schottky diode [Operating Speed is high]
74HC00, Where 'HC' implies High Speed CMOS
74HCT00, Where 'HCT' implies High speed CMOS with TTL compatible...

Let me conclude
CMOS - Low Speed Low Power Consumption
TTL - High Speed High Power Consumption
CHMOS - High Speed Low power Consumption

 

[keith1200rs]

Have a look at this link Logic Voltage Thresholds for TTL, CMOS, LVCMOS, and GTLP IC families

You need to carefully look at the triggering thresholds of the logic inputs and the voltage levels of the outputs to decide what works with what. Optocouplers are not the way to do conversion - they are large, slow and consume too much power.

TTL thresholds imply 0.8V for a low and around 2V for a logic high (on a 5V supply). A CMOS chip driving a TTL chip will have no problems. A TTL chip driving a CMOS chip will not pull the output high enough.

Keith.

 

[myatham]

Hi,

Is it possible to have TTL levels for a CMOS IC?

 

[keith1200rs]

Yes. Any of the 74HCTxxx series ICs for example are TTL wherea the 74HCxxx ones are CMOS levels.

Keith.