The difference between TTL level, CMOS level, RS232 level

What is TTL level, CMOS level, RS232 level? What difference do they have? Generally, the CMOS level has a higher noise tolerance than the TTL level.

(i), TTL level standard
Output L: <0.8v; h:>2.4v.
Input L: <1.2v; h:>2.0v
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.

(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.

(iii), RS232 standard
The level of logic 1 is -3~-15v, the logic 0 is +3~+15v, and the definition of the level is reversed once.

What is the difference between using 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.

4. Many devices are compatible with TTL and CMOS, datasheet will be described. If speed and performance are not considered, general devices can be interchanged. However, it is important to note that sometimes the load effect may cause the circuit to work abnormally, because some TTL circuits require the next level of input impedance as the load to function properly.

1. Logic level of TTL circuit and CMOS circuit

VOH: Output voltage of logic level 1

VOL: Output voltage of logic level 0

VIH: Input voltage of logic level 1

VIH: Input voltage of logic level 0

TTL Circuit Critical value:

Vohmin = 2.4V Volmax = 0.4V

Vihmin = 2.0V Vilmax = 0.8V

CMOS circuit critical value (supply voltage is + +)

Vohmin = 4.99V Volmax = 0.01V

Vihmin = 3.5V Vilmax = 1.5V

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.

3. Common logic Chip features

74LS series: TTL input: TTL output: TTL

74HC series: CMOS input: CMOS output: CMOS

74HCT series: CMOS input: TTL output: CMOS

CD4000 series: CMOS input: CMOS output: CMOS

The difference between TTL level, CMOS level, RS232 level