Since I learned to write machine code this way, I'll add a little bit of color.
You can take the instruction set of a simple microprocessor, and lay out its instruction set in a tabular format. This made it relatively easy to see the correspondence between an instruction in assembly language and its numerical code.
Handy "reference cards" were published for looking up the codes, printed on nice thick plastic. You can find these in a google image search for your favorite micro. I got by with a photocopy. Along with that, a programmer would have their own notes and diagrams taped to the walls for quick reference. Machines were simple enough that you really could have all of the vital information available at a glance.
Today, the "datasheet" for a sophisticated 32 bit microcontroller is many thousands of pages.
Microprocessors had relatively few transistors by today's standards, so the instruction decode logic had to be simple. Logical, if I may say so. This resulted in being able to describe operators and their operands as blocks of bits in an instruction word.
I arrived late enough in the game that personal computers already existed, yet I got myself started by hand assembling for the microprocessor circuits that I brought up from scratch.
You can take the instruction set of a simple microprocessor, and lay out its instruction set in a tabular format. This made it relatively easy to see the correspondence between an instruction in assembly language and its numerical code.
Handy "reference cards" were published for looking up the codes, printed on nice thick plastic. You can find these in a google image search for your favorite micro. I got by with a photocopy. Along with that, a programmer would have their own notes and diagrams taped to the walls for quick reference. Machines were simple enough that you really could have all of the vital information available at a glance.
Today, the "datasheet" for a sophisticated 32 bit microcontroller is many thousands of pages.
Microprocessors had relatively few transistors by today's standards, so the instruction decode logic had to be simple. Logical, if I may say so. This resulted in being able to describe operators and their operands as blocks of bits in an instruction word.
I arrived late enough in the game that personal computers already existed, yet I got myself started by hand assembling for the microprocessor circuits that I brought up from scratch.