4. EMBEDDED SYSTEMS The Embedded system is a combination of software and hardware designed to perform a specific function.It may use a micro processor or a micro controller to perform the task A Micro-controller is a processor with an on chip RAM, ROM, Timer, and I/O ports. Micro processors do not contain RAM, ROM, and I/O ports on the chip.They have to connected externally which makes them bulkier and costlier.

5. 8051 is a 8-bit micro controller introduced by Intel Corp in 1981. It had 128 byte of RAM, 4K bytes of on-chip ROM, two timers,one serial port and four ports each of 8-bit wide on single chip.As it is 8-bit micro controller only 8 bits data can be processed at a time. 8051 has a total of 5+1 Interrupt sources, 5 software and 1 hardware. 8051 FAMILY

8. ĒĀ: External access, used mainly in 8031 family to connect to external memory, where it connected to GND. ĒĀ – 0 external memory, ĒĀ – 1 internal memory program store enable, used to access the program code stored in external memory. ALE: Address latch enable, O/P, active high. It is used in 8031 which multiplexes address and data on port 0,which is connected to external memory. PORTS: All the four ports are 8-bit ports. On RESET all the ports are configured as output. PORT0: It occupies pins from 32-39 and can be used for I/P or O/P. It is designated as AD0 – AD7 for both address and data when an external memory is connected. ALE=0 it provides data D0 – D7,when ALE=1, it provides address A0 – A7.

9. PORT1: Port1can also be used as I/O and O/P. It is also a 8-bit port occupying pins 1 – 8. PORT2: Port2 occupies pins 21 – 28 .It can be used as I/O and O/P. It is also used as A8 – A15, address lines when connected to an external memory. Along with port0 it provides the 16-bit address to the external memory. PORT3: It occupies pins 10 – 17 and can be used as I/O or O/P. Port3 has additional functions like interrupts, read, write, timers etc., The pins P3.0 and P3.1 are used for serial communication, P3.2 and P3.3 are used for external interrupts, P3.4 and P3.5 are used for timers and P3.6and P3.7 are used to write and read signals of external memories connected in 8031-based system. All the ports of 8051 family are bit addressable.

15. ANY DOUBTS??????????????