Robert Revens said:Seriously, not knowing assembler is going to severely limit your progress with the 8051 (IMHO).
Learning how to use the internet wisely is the important lesson.
cheap fatty sausage
whatever you get from the net is worthless un less you are able to code the routine(s) yourself. If you do not have the capability to fully understand the routine(s) you will be stuck with "the little fix" that always is required to use downloaded stuff

You will seldom need to write ASM for most modern microcontrollers. However it is useful to be able to read ASM on occasions to understand the efficiency of a HLL compiler.
if you need to "understand the efficiency" you should not use C in the first place, Even more important is that you are able to "think ASM" since 'C' assumes that all I/O is taken care of (fopen - fread - ...) and I/O is so close to the hardware that "thinking C" will get you lost. I am NOT discussing what language to write it in, I am discussing the mindset.

using debugged library code
even 'debugged' (it often is not) you still, in most cases, need to adapt a bit, thus 'using' is crap, 'understanding' is correct.

Erik