Eng.Samra Essalaimeh Philadelphia University 2013/ nd Semester PIC Microcontrollers

Microelectronic Devices Digital Devices: A+5V supply, usually derived from the mains, is therefore required to power the circuits. It must be able to provide sufficient current for the processor circuits, at a voltage which must be between 4.75V and 5.25V for standard TTL (Transistor–Transistor Logic).

FET Logic Gates: The FET is the basic switching device which appears in the PIC data sheet in the equivalent circuits for various functional blocks. It is a transistor which works as a current switch; current flow through a semiconductor ‘channel’ is controlled by the voltage at the input ‘gate’.

Logic Circuits: There are no actual resistors used because they waste too much power; instead, other FETs are used as ‘active loads’, which reduces the power which would be dissipated as heat in the resistors. Digital circuits are based on various combinations of these logic gates, fabricated on a silicon wafer.

Logic Gates:

Combinational Logic: Combinational logic describes circuits in which the output is determined only by the current inputs, and not by the inputs at some previous point in time. Binary addition is a basic function of the arithmetic and logic unit (ALU) in any microprocessor. Simple Binary Adder

Full Adder Full adder logic table Full adder logic circuit

4-Bit Adder

Sequential Logic: Sequential logic refers to digital circuits whose outputs are determined by the current inputs AND the inputs which were present at an earlier point in time. Basic Latch

Data Latch

Data latch timing diagram.

Data Devices All data processing or digital control systems have circuits to carry out the following operations: 1. data input 2. data storage 3. data processing 4. data output 5. control and timing Data Input Switch:

Tri-State Gate: Data Latch LED Data Display

Simple Data System

4-Bit Data System

Digital Systems 4.1 Encoder and Decoder 4.2 Multiplexer, Demultiplexer and Buffer 4.3 Registers and Memory 4.4 Memory Address Decoding 4.5 System Address Decoding 4.6 Counters and Timers 4.7 Serial and Shift Registers 4.8 Arithmetic and Logic Unit 4.9 Processor Control

Encoder and Decoder Hexadecimal key pad operation 2-bit decoder logic table; 2-bit encoder logic table.

Multiplexer, Demultiplexer and Buffer

Registers and Memory

Memory Address Decoding

System Address Decoding As we have seen, there are usually several memory and input/output devices connected to a common data bus in the typical microprocessor system. Only one can use the data bus at any one time, so a system of chip selection is needed, so that the processor can ‘talk to’ the required peripheral chip. A typical memory map for a system with a 16-bit address bus (four hex digits) is shown in Table 4.2. The I/O is memory mapped, that is, the port registers are placed in the same address space as the memory. Notice that not all the available addresses have to be used. Go back to the figure

Counters and Timers

Serial and Shift Registers Arithmetic and Logic Unit

Processor Control