74LSxxxx is a Low power Schottky process 74HCxxxx is a High speed CMOS process Both functions are the same, there are some differences in specifications 74LS power supply voltage VCC 5V \/ -5%, 74HC Supply voltage VCC 2.0 ~ 6.0V Input voltage High (ViH) 74LS is 2.0V, 74HC is 3.5V Input voltage Low (ViL) 74LS is 0.8V, 74HC is 1.5V output voltage High (VoH) 74LS is 2.7Vmin, 74HC is VDD-0.1V Output voltage Low (VoL) 74LS is 0.5V, 74HC is 0.1V static current consumption 74LS is 0.4mA, 74HC is 0.0005mA transmission delay Tp 74LS is 9.0ns,74HC is 8.0ns74LS relatively power consumption, driving capacity is also relatively strong, if the power consumption is not considered, 74LS14 can replace 74HC14.