8051 Serial communication - Microcontroller Programming and Embedded Systems


Serial Communication is a form of I/O in which the bits of a byte being transferred appear one after other in a timed sequence on a single wire. Serial Communication uses two methods, asynchronous and synchronous. The Synchronous method transfers a block of data at a time, while the asynchronous method transfers a single byte at a time. In Synchronous Communication the data get transferred based on a common clock signal. But in Asynchronous communication, in addition to the data bit, one start bit and one stop bit is added. These start and stop bits are the parity bits to identify the data present between the start and stop bits.

The 8051 has two pins that are used specifically for transferring and receiving data serially. These two pins are called TXD and RXD and are part of the Port-3 group (Port-3.0 and Port-3.1). Pin 11 of the 8051 is assigned to TXD and pin 10 is designated as RXD. These pins are TTL compatible; therefore they require a line driver to make them RS232 compatible. The line driver chip is MAX232. The MAX232 uses +5v power source, which is same as the source voltage for 8051.

8051 Interrupts Programming - Microcontroller Programming and Embedded Systems


Interrupt is one of the most important and powerful concepts and features in Microcontroller / processor applications. Almost all the real world and real time systems built around microcontrollers and microprocessors make use of interrupts.
What is Interrupt
The interrupts refer to a notification, communicated to the controller, by a hardware device or software, on receipt of which controller momentarily stops and responds to the interrupt. Whenever an interrupt occurs the controller completes the execution of the current instruction and starts the execution of anInterrupt Service Routine (ISR) or Interrupt Handler. ISR is a piece of code that tells the processor or controller what to do when the interrupt occurs. After the execution of ISR, controller returns back to the instruction it has jumped from (before the interrupt was received). The interrupts can be either hardware interrupts or software interrupts.
Why need interrupts
An application built around microcontrollers generally has the following structure. It takes input from devices like keypad, ADC etc; processes the input using certain algorithm; and generates an output which is either displayed using devices like seven segment, LCD or used further to operate other devices like motors etc. In such designs, controllers interact with the inbuilt devices like timers and other interfaced peripherals like sensors, serial port etc. The programmer needs to monitor their status regularly like whether the sensor is giving output, whether a signal has been received or transmitted, whether timer has finished counting, or if an interfaced device needs service from the controller, and so on. This state of continuous monitoring is known as polling.

In polling, the Microcontroller keeps checking the status of other devices; and while doing so it does no other operation and consumes all its processing time for monitoring. This problem can be addressed by using interrupts. In interrupt method, the controller responds to only when an interruption occurs. Thus in interrupt method, controller is not required to regularly monitor the status (flags, signals etc.) of interfaced and inbuilt devices.

8051 Interfacing to External Memory


Real-World Interfacing I, LCD, ADC, and SENSORS


LCD and Keyboard Interfacing


8031-51 interfacing with the 8255





Real Time Spectrum Analysis


Fundamentals of Real Time Spectrum Analysis.

A Real Time Analyzer (RTA) is a professional audio device that measures and displays the frequency spectrum of an audio signal; a spectrum analyzer that works in real time. An RTA can range from a small PDA-sized device to a rackmounted hardware unit to software running on a laptop. It works by measuring and displaying sound input, often from an integrated microphone or with a signal from a PA system. Basic RTAs show three measurements per octave at 3 or 6 dB increments; sophisticated software solutions can show 24 or more measurements per octave as well as 0.1 dB resolution.....................

Datapath Logic Cells and I/O Cells | Cell Compilers


Datapath Logic Cells
Suppose we wish to build an n -bit adder (that adds two n -bit numbers) and to exploit the regularity of this function in the layout. We can do so using a datapath structure.
The following two functions, SUM and COUT, implement the sum and carry out for a full adder ( FA ) with two data inputs (A, B) and a carry in, CIN:  
COUT = A · B + A · CIN + B · CIN = MAJ(A, B, CIN).
The sum uses the parity function ('1' if there are an odd numbers of '1's in the inputs). The carry out, COUT, uses the 2-of-3 majority function ('1' if the majority of the inputs are '1'). We can combine these two functions in a single FA logic cell, ADD(A[ i ], B[ i ], CIN, S[ i ], COUT), shown in Figure 2.20(a), where  
S[ i ] = SUM (A[ i ], B[ i ], CIN) ,

Types of ASICs


Types of ASICs

ICs are made on a thin (a few hundred microns thick), circular silicon wafer , with each wafer holding hundreds of die (sometimes people use dies or dice for the plural of die). The transistors and wiring are made from many layers (usually between 10 and 15 distinct layers) built on top of one another. Each successive mask layer has a pattern that is defined using a mask similar to a glass photographic slide. The first half-dozen or so layers define the transistors. The last half-dozen or so layers define the metal wires between the transistors (the interconnect ).
A full-custom IC includes some (possibly all) logic cells that are customized and all mask layers that are customized. A microprocessor is an example of a full-custom IC—designers spend many hours squeezing the most out of every last square micron of microprocessor chip space by hand. Customizing all of the IC features in this way allows designers to include analog circuits, optimized memory cells, or mechanical structures on an IC, for example. Full-custom ICs are the most expensive to manufacture and to design. The manufacturing lead time (the time it takes just to make an IC—not including design time) is typically eight weeks for a full-custom IC. These specialized full-custom ICs are often intended for a specific application, so we might call some of them full-custom ASICs....

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