07-08-2014, 02:54 PM
PRE-SCHEDULED INDUSTRIAL APPLIANCES USING RTC
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INTRODUCTION
A Micro controller consists of a powerful CPU tightly coupled with memory, various I/O interfaces such as serial port, parallel port timer or counter, interrupt controller, data acquisition interfaces-Analog to Digital converter, Digital to Analog converter, integrated on to a single silicon chip.
If a system is developed with a microprocessor, the designer has to go for external memory such as RAM, ROM, EPROM and peripherals. But controller is provided all these facilities on a single chip. Development of a Micro controller reduces PCB size and cost of design.
One of the major differences between a Microprocessor and a Micro controller is that a controller often deals with bits not bytes as in the real world application.
Intel has introduced a family of Micro controllers called the MCS-51.
Types of memory
The 89C51 have three general types of memory. They are on-chip memory, external Code memory and external Ram. On-Chip memory refers to physically existing memory on the micro controller itself. External code memory is the code memory that resides off chip. This is often in the form of an external EPROM. External RAM is the Ram that resides off chip. This often is in the form of standard static RAM or flash RAM.
Internal RAM
The 89C51 have a bank of 128 of internal RAM. The internal RAM is found on-chip. So it is the fastest Ram available. And also it is most flexible in terms of reading and writing. Internal Ram is volatile, so when 89C51 is reset, this memory is cleared. 128 bytes of internal memory are subdivided. The first 32 bytes are divided into 4 register banks. Each bank contains 8 registers. Internal RAM also contains 128 bits, which are addressed from 20h to 2Fh. These bits are bit addressed i.e. each individual bit of a byte can be addressed by the user. They are numbered 00h to 7Fh. The user may make use of these variables with commands such as SETB and CLR.
Flash memory is a nonvolatile memory using NOR technology, which allows the user to electrically program and erase information. Flash memory is used in digital cellular phones, digital cameras, LAN switches, PC Cards for notebook computers, digital set-up boxes, embedded controllers, and other devices
ALE/PROG
Address Latch Enable output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation ALE is emitted at a constant rate of 1/6the oscillator frequency, and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external Data Memory.
If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the micro controller is in external execution mode
Memory organization of RAM
This is a common name for the total 8 general purpose registers (R0, R1, R2 ...R7). Even they are not true SFRs, they deserve to be discussed here because of their purpose. The bank is active when the R registers it includes are in use. Similar to the accumulator, they are used for temporary storing variables and intermediate results. Which of the banks will be active depends on two bits included in the PSW Register. These registers are stored in four banks in the scope of RAM
How stacks are accessed in the 8051
If the stack is a section of RAM, there must be registers inside the CPU to point to it. The register used to access the stack is called the SP (Stack point) Register. The stack pointer in the 8051 is only 8 bits wide; which means that it can take values of 00 to FFH. When the 8051 is powered up, the SP register contains value 07. This means that RAM location 08 is the first location used for the stack by the 8051. The storing of a CPU register in the stack is called a PUSH, and pulling the contents off the stack back into a CPU register is called a POP. In other words, a register is pushed onto the stack to save it and popped off the stack to retrieve it. The job of the SP is very critical when push and pop actions are performed.
TIMERS
On-chip timing/counting facility has proved the capabilities of the micro controller for implementing the real time application. These includes pulse counting, frequency measurement, pulse width measurement, baud rate generation, etc,. Having sufficient number of timer/counters may be a need in a certain design application. The 8051 has two timers/counters. They can be used either as timers to generate a time delay or as counters to count events happening outside the micro controller.
Serial Communication
Serial data 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 data transmission if the data can be transmitted and received, it is a duplex transmission. This is in contrast to simplex transmissions such as with printers, in which the computer only sends data. Duplex transmissions can be half or full duplex, depending on whether or not the data transfer can be simultaneous. If data is transmitted one way at a time, it is referred to as half duplex. If the data can go both ways at the same time, it is full duplex. Of course, full duplex requires two wire conductors for the data lines, one for transmission and one for reception, in order to transfer and receive data simultaneously.
INTERRUPTS vs POLLING
The advantage of interrupts is that the micro controller can serve many devices (not all the same time, of course); each device can get the attention of the micro controller based on the priority assigned to it. The polling method cannot assign priority since it checks all devices in round-robin fashion. More importantly, in the interrupt method the micro controller can also ignore (mask) a device request for service. This is again not possible with the polling method. The most important reason that the interrupt method is preferable is that the polling method wastes much of the micro controller’s time by polling devices that do not need service. So, in order to avoid tying down the micro controller, interrupts are used
Power supply
The power supply are designed to convert high voltage AC mains electricity to a suitable low voltage supply for electronics circuits and other devices. A power supply can by broken down into a series of blocks, each of which performs a particular function. A d.c power supply which maintains the output voltage constant irrespective of a.c mains fluctuations or load variations is known as “Regulated D.C Power Supply”
For example a 5V regulated power supply system as shown below:
Capacitor Filter
We have seen that the ripple content in the rectified output of half wave rectifier is 121% or that of full-wave or bridge rectifier or bridge rectifier is 48% such high percentages of ripples is not acceptable for most of the applications. Ripples can be removed by one of the following methods of filtering:
(a) A capacitor, in parallel to the load, provides an easier by –pass for the ripples voltage though it due to low impedance. At ripple frequency and leave the d.c.to appears the load.
(b) An inductor, in series with the load, prevents the passage of the ripple current (due to high impedance at ripple frequency) while allowing the d.c (due to low resistance to d.c)
© various combinations of capacitor and inductor, such as L-section filter section filter, multiple section filter etc. which make use of both the properties mentioned in (a) and (b) above. Two cases of capacitor filter, one applied on half wave rectifier and another with full wave rectifier.
Regulator
Voltage regulator ICs is available with fixed (typically 5, 12 and 15V) or variable output voltages. The maximum current they can pass also rates them. Negative voltage regulators are available, mainly for use in dual supplies. Most regulators include some automatic protection from excessive current ('overload protection') and overheating ('thermal protection'). Many of the fixed voltage regulator ICs have 3 leads and look like power transistors, such as the 7805 +5V 1A regulator shown on the right. The LM7805 is simple to use. You simply connect the positive lead of your unregulated DC power supply (anything from 9VDC to 24VDC) to the Input pin, connect the negative lead to the Common pin and then when you turn on the power, you get a 5 volt supply from the output pin
Basic Theory
H-bridge. Sometimes called a "full bridge" the H-bridge is so named because it has four switching elements at the "corners" of the H and the motor forms the cross bar.
The key fact to note is that there are, in theory, four switching elements within the bridge. These four elements are often called, high side left, high side right, low side right, and low side left (when traversing in clockwise order).
The switches are turned on in pairs, either high left and lower right, or lower left and high right, but never both switches on the same "side" of the bridge. If both switches on one side of a bridge are turned on it creates a short circuit between the battery plus and battery minus terminals. If the bridge is sufficiently powerful it will absorb that load and your batteries will simply drain quickly. Usually however the switches in question melt.
To power the motor, you turn on two switches that are diagonally opposed. In the picture to the right, imagine that the high side left and low side right switches are turned on.
The current flows and the motor begins to turn in a "positive" direction. Turn on the high side right and low side left switches, then Current flows the other direction through the motor and the motor turns in the opposite direction
SOFTWARE DESCRIPTION
It is possible to create the source files in a text editor such as Notepad, run the Compiler on each C source file, specifying a list of controls, run the Assembler on each Assembler source file, specifying another list of controls, run either the Library Manager or Linker (again specifying a list of controls) and finally running the Object-HEX Converter to convert the Linker output file to an Intel Hex File. Once that has been completed the Hex File can be downloaded to the target hardware and debugged. Alternatively KEIL can be used to create source files; automatically compile, link and covert using options set with an easy to use user interface and finally simulate or perform debugging on the hardware with access to C variables and memory. Unless you have to use the tolls on the command line, the choice is clear. KEIL Greatly simplifies the process of creating and testing an embedded application.