AN887 Datasheet, PDF (2/12 Pages) STMicroelectronics – MICROCONTROLLERS MADE EASY

MICROCONTROLLERS MADE EASY
Flash
Flash is an electrically erasable and programmable memory. It can be used instead of ROM to
store program instructions and data. A key parameter of Flash memory is its endurance or the
number of times it can be erased or reprogrammed. Depending on the technology used, flash
endurance can be either 100 or 300,000 program/erase cycles.
RAM (Random Access Memory)
During in the execution of a program, data have to be saved for later use. Data are usually
stored in RAM.
EEPROM (Electrically Erasable Programmable Read Only Memory)
There is another way to store data in a microcontroller: EEPROM is used to store data that
must be saved through a power down cycle.
CPU (Central Processing Unit)
It is the brain of the system that processes all data and their travel along the bus. For example,
in order to execute a program, the CPU will read the first instruction from program memory.
This instruction is decoded by the CPU and executed. At the completion of the execution of
the instruction, the next instruction is fetched from memory and is executed. This procedure is
repeated until the end of the program (or an endless loop) is found.
Figure 2. Typical Microcontroller Block Organization
INPUT
OUTPUT
PERIPHERAL
SYSTEMS
BUS
CENTRAL
PROCESSING
UNIT
TIMING
SYSTEM
PROGRAM
MEMORY
ROM
DATA
MEMORY
RAM
EEPROM
VR02101B
TIMERS
The timer or timing system makes it possible to measure and time external and internal
events. The power of the timers varies greatly between different MCUs.
I / O (INPUT / OUTPUT) PORTS
Most microcontrollers have several digital I/O ports that are used to drive a LED or get a key-
board input. Usually, a port consists of eight or less bits, usually programmable as either input
or output bits.
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