Understanding of the various levels

TTL level signals are used most often because the data is usually expressed in binary terms, which is equivalent to the logic "1", 0V is equivalent to the logic "0", which is called TTL (transistor-transistor logic level) signaling system

"TTL level" is most commonly used in the relevant electrical majors, such as: circuit, digital circuit, microcomputer principle and interface technology, microcontroller and other courses are involved. There are only two levels in the digital circuit (high and low) high-level, low-level 0V. Also widely used are CMOS level, 232 level, 485 power parity.with CMOS tube

2. CMOS is a FET structure, TTL is a bipolar transistor 2.CMOS logic level range is larger (3~15v), TTL can only operate at 5V 3. CMOS high and low differences between the high, anti-jamming, TTL is small , anti-jamming ability of 4.CMOS power consumption is very small, TTL power (1~5ma/door) 5.CMOS operating frequency than TTL slightly lower, but the speed of the CMOS speed and TTL almost equal
4. (i), TTL level standard  
   output L: < 0.8V; h:>2.4v. &NBSP;
   input L: <1.2v; h:>2.0v &NBSP;
   TTL device output low to less than 0.8V, high level is greater than 2.4V. Input, less than 1.2V is considered to be 0, above 2.0 is considered to be 1. The noise tolerance of the input low level of the TTL level is only (0.8-0)/2=0.4v, and the noise tolerance for the high level is (5-2.4)/2=1.3v.
6. (ii), CMOS level standard
   output L: <0.1*VCC; h:>0.9*vcc.  
   input L: <0.3*VCC; h:>0.7*vcc.  
   Since the CMOS power supply is 12V, the input is lower than 3.6V, the noise tolerance is 1.8V, higher than 3.5V is high, and the noise tolerance is higher than 1.8V. There is a higher noise tolerance than TTL.

8. (c), RS232 standard logic 1 level of -3~-15v, logic 0 level of +3~+15v, pay attention to the definition of the level is reversed once.

   What is the difference between TTL and CMOS level 1. The upper and lower limits of the level are defined differently, and the CMOS has a larger noise-cancelling area. The same is 5 volts power supply, TTL is generally 1.7V and 3.5V appearance, CMOS is generally 2.2v,2.9v appearance, inaccurate, for reference only.

   2. The current drive capacity is not the same, TTL generally provides 25 MA drive capacity, and CMOS generally at about 10 Ma.

   3. The required current input size is also different, the general TTL needs about 2.5 mah, CMOS hardly need current input.

10. 2. Logic level translation for TTL and CMOS

    CMOS level can drive TTL level

    The TTL level does not drive the CMOS level and requires a pull resistor.

Understanding of the various levels