transmission from the CPU to the printer is done in what form?

Answer 1

There may be information in here that'll help. If not, re-search in the How Stuff Works website, using different search terms.

http://computer.howstuffworks.com/pc3.htm

http://electronics.howstuffworks.com/microcontroller1.htm

http://computer.howstuffworks.com/operating-system2.htm