JiffyMON/64 is a unique and powerful machine language monitor for Commodore 64 and 128 (in 64 mode) computers equipped with the JiffyDOS speed-enhancement ROMs. Like other machine language monitors, JiffyMON lets you inspect and modify individual bytes in your computer's memory; assemble, disassemble, and execute 6510 assembler code programs; and also provides a number of features which assist in debugging and writing assembly language programs.

This fully re-typed and improved manual came from the excellent slark.me/c64 website.  Please visit them and check out the other fine reference material