Rewriting flash memory in user program mode using asynchronous serial communication

What is flash memory?
Flash is rewritable storage chip that holds content without power. Flash memory chips can either be NOR or NAND.

What is memory?
It is the computer's physical workspace that stores the instructions, programs and data needed to accomplish the tasks executed by the processor for some interval of time, even after electrical power to the computer is turned off.

What does asynchronous mean?
In an asynchronous circuit, parts are largely autonomous. They are not governed by any regular, periodic time-controlling mechanism, such as a clock circuit or signal, but instead need only wait for the signals that indicate completion of instructions and operations. These signals are often specified by simple data transfer protocols.
This digital logic design is contrasted with a synchronous circuit which operates according to clock timing signals.