Do you have a PC that you can boot into true MS-DOS; ie, not the DOS-replacement "command prompt" in Windoze?

If so, prepare a plain, unformatted, pure ASCII text file (ending with a formfeed), and then do

copy file.txt LPT1:

or whatever.

Try this with your dot-matrix, inkjet, and laser printers.

The MS-DOS copy does not use any drivers, and does not add any initialisation - it just copies the bytes from the file to the port verbatim.
So, if your laser print works like this, you'll know that it's something wrong with your 8051 stuff; if your laser printer still doesn't work like this, you'll know that it's something to do with the printer - either it's faulty, or not set up properly.