Specifications

mikroElektronika | Free Online Book | PIC Microcontrollers | Introduction: World of Microcontrollers
● Instruction Decoder is a part of the electronics which recognizes program instructions and runs other circuits on the basis of that. The
“instruction set” which is different for each microcontroller family expresses the abilities of this circuit.
● Arithmetical Logical Unit (ALU) performs all mathematical and logical operations upon data.
● Accumulator is a SFR closely related to the operation of the ALU. It is a kind of working desk used for storing all data upon which some
operation should be performed (addition, shift/move etc.). It also stores the results ready for use in further processing. One of the SFRs,
called a Status Register (PSW), is closely related to the accumulator. It shows at any given moment the “status” of a number stored in the
accumulator (number is greater or less than zero etc.).
Fig. 0-22 Central Processor Unit - CPU
Bus
Physically, the bus consists of 8, 16 or more wires. There are two types of buses: the address bus and the data bus. The address bus consists of as
many lines as necessary for memory addressing. It is used to transmit the address from the CPU to the memory. The data bus is as wide as the
data, in our case it is 8 bits or wires wide. It is used to connect all circuits inside the microcontroller.
Serial Communication
Parallel connections between the microcontroller and peripherals via input/output ports is the ideal solution for shorter distances- up to several
meters. However, in other cases - when it is necessary to establish communication between two devices on longer distances it is not possible to
use a parallel connection - such a simple solution is out of question. In these situations, serial communication is the best solution.
Today, most microcontrollers have built in several different systems for serial communication as a standard equipment. Which of these systems
will be used depends on many factors of which the most important are:
● How many devices the microcontroller has to exchange data with?
● How fast the data exchange has to be?
● What is the distance between devices?
● Is it necessary to send and receive data simultaneously?
One of the most important things concerning serial communication is the Protocol which
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