Re: 89s52 learning board
Hi! The main thing is switching voltage value. LS series are working like an ordinary TTL ("L" below 0.8, "H" from 2.4 up to VCC). HC series is working like CMOS ("L" below 0.8V, "H" - I am not quite sure - about 90% of VDD). The next is power consumption. But I think you can find details using f.e. Google web site.
Most NMOS accept TTL level on its inputs and can drive one TTL load on its outputs. Some CMOS accept TTL level, but some others not.
Also same devices from different manufacturers can have different input or output levels. Also different pins on a device can have different input or output levels. To drive HC from LS or NMOS you need pull up resistors.
I prefer HCTL but sometimes I have been using HC instead of HCT. Sometimes I have been using LS instead of HCT. But all depends on your application.
Sounds really confusing ?
Yes, no common rule exist !
So you must compare the data sheets of every device, which you want to use.