Microprocessor is a device which can handle complex calculation and control strategies, it can receive low level signal from sensors and convert to digitalwhich can be transmitted into long distance.
Advantages of Microprocessor Based Control:
1.Low-level singal from sensors, once converted to digital, can be transmitted long distances virtually error-free.
2.A microprocessor can handle complex calculations and control stratgies.
3.Changing the control stratgey is easy by loading in a new program; no hardware changes are required.
4.Microprocessor based controllers can be easily connected to computer networks within an organization. This allows the designers to enter program changes and read current status fro their desk terminals.
5.long-term memory is available to keep track of parameters in slow-moving systems.
Arithmetic logic unit (ALU):
ALU is responsible foR performing arithmetic and logical operations. It also keeps track of status flags
that tell subsequent instructions whether the result was positive,negative, or zero, and whether an addition or subs traction operationcreated a carry or borrow.
Memory:
Microprocessors require memory resources to store programs and data. Memory can be classified two broad categories:
Volitile - loses its contents when power is turned off &
Non-volatile - can retain its contents even if power is turned off.
1 Read Only Memory (ROM):
Programmable Read Only Memory (PROM)
Erasable Programmable ROM (EPROM)
Electrically Erasable Programmable ROM (EEPROM)
2 Random Access Memory (RAM):
Dynamic Random Access Memory (DRAM)
Static Random Access Memory (SRAM)
3 Other Forms of Memory:
Cache Memory
Flash Memory
Video Memory (VRAM)
Read Only Memory:
The ROM, also known as firmware, cannot be written on or erased using the computer. ROM chips contain programs that are set in at the factory; these are special instructions for computer operations. ROM chips do not loose their contents when power is removed.
PROM - can be programmed using special equipment. Once the program is written, it cannot be erased.
EPROM - are like ROM chips except that the contents can be erased, and the new data can be written. Erasure is done with a special device that uses UV light.
EEPROM - can be reprogrammed using special electrical impulses. The advantages of EEPROM chips is that they need notto be removed from the computer to be changed.
andom Access Memory:
he RAM, also known as internal memory, primary storage or
mply memory. It has three basic tasks:
1 It holds the data for processing.
2 It holds the instructions (programs).
3 It holds the data after it is processed & waiting to be sent to a
output or storage.
The contents of the RAM address locations change continually computer executes a program. It requires fast READ and WR cycle times so as no to slow down the computer operation. A major disadvantage of RAMs is that they are volatile and lo all the stored information if power is interrupted.
Other Memories:
Cache Memory - These are usually built into the MPU chip. These allows the CPU to run faster because it does not have to take time to swap instructions in and out of the RAM. The most frequently used instructions are kept in the cache memory so the CPU can look there fast.
Flash Memory - Consists of circuitry on credit-card-size card that can be inserted into slots connecting to the PC motherboard. These are non-volatile memory. These are becoming very popular in microprocessor/micro controller based applications.
Video Memory - chips used to store display images for the monitor. The amount of video memory determines how fast images appear and how many colors are available.
Input/Output Units:
The I/O operation is defined as the transfer of data between the MPU and the external world. The term peripheral devices is used for the pieces of equipment that exchange data with a MPU
system.
In input operations the input device places the data in the data register of the interface chip to hold until it is read by the MPU In output operations, the MPU places the data in the register until it is read by the peripheral.
As the speeds and characteristics of peripheral devices can differ significantly from those of the MPUs, these are connected via interface chips to synchronize data transfers between MPU and the peripheral devices.
Buses:
There are three buses external to the MPU and two buses within MPU. The external address and data buses are the extension of the same buses inside the MPU.
1.
Address Bus - is a 16-line unidirectional bus that carries 16-bit address code from the MPU to the memory unit to select the memory location which the MPU is accessing for a READ or WRITE operation.
2.
Data Bus - is a 8-line bidirectional bus over which 8-bit words can be sent from the MPU to the memory or from the memory to the MPU. It can carry data/instruction codes.
3.
Control Bus - is grouping of all the timing and control signals needed to synchronize the operation of MPU with the other units of the microcomputer.
