8051 microcontrollers

802 8 6 MICROPROCESSOR 8.1 Salient Features of 80286 The 80286 is the first member of the family of advanced microprocessors with memory management and protection abilities. The 80286 CPU, with its 24-bit address bus is able to address 16 Mbytes of physical memory. Various versions of 80286 are available that runs on 12.5 MHz , 10 MHz and 8 MHz clock frequencies. 80286 is upwardly compatible with 8086 in terms of instruction set. 80286 has two operating modes namely real address mode and virtual address mode. In real address mode, the 80286 can address upto 1Mb of physical memory address like 8086. In virtual address mode, it can address up to 16 Mb of physical memory address space and 1 Gb of virtual memory address space. The instruction set of 80286 includes the instructions of 8086 and 80186. 80286 has some extra instructions to support operating system and memory management. In real address mode, the 80286 is object code compatible with 8086. In protected virtual address mo...

8.4 RS 232 Serial Communication Standards In serial I/O, data can be transmitted as either current or voltage. When data is transmitted as voltage, the commonly used standard is known as RS-232C. This standard was developed by Electronic Industries Association (EIA), USA and adopted by IEEE. RS-232 standard proposes a maximum of 25 signals for the bus used for serial data transfer. 8.4.1 RS-232 Pin Names and Signal Descriptions Pin Number Common Name RS-232 Name Description 1 - AA Protective Ground 2 TxD BA Transmitted Data 3 RxD BB Received Data ...

8.3 NUMERIC DATA PROCESSOR 8087 The numeric data processor is a coprocessor which has been designed to work under the control of the 8086 processor. It offers additional numeric processing capabilities. It is available in 5 MHz, 8 MHz and 10 MHz versions 8086 will perform the opcode fetch cycles and identify the instructions for 8087. Once the instruction is identified by 8086, it is allotted to 8087 for further execution. 8086-8087 couplet implements instruction level master-slave configuration. After the completion of the 8087 execution cycle, the results may be referred back to the CPU. The 8087 instructions may lie interleaved in the 8086 program as if they belong to the 8086 instruction set. It is the task of 8086 to identify the 8087 instructions from the program, send it to the 8087 for execution and get back the results. The 8087 adds 68 new instructions to the instruction set of 8086. 8.3.1 Architecture of 8087 F ig. 8.10 8087 Architecture 8087 is divided interna...

8.2 SERIAL COMMUNICATION USING 8251 8251 is a Universal Synchronous and Asynchronous Receiver and Transmitter compatible with Intel’s processors. This chip converts the parallel data into a serial stream of bits suitable for serial transmission. It is also able to receive a serial stream of bits and convert it into parallel data bytes to be read by a microprocessor. 8.2.1 Basic Modes of data transmission a) Simplex b) Duplex c) Half Duplex a) Simplex mode Data is transmitted only in one direction over a single communication channel. For example, the processor may transmit data for a CRT display unit in this mode. b) Duplex Mode In duplex mode, data may be transferred between two transreceivers in both directions simultaneously. c) Half Duplex mode In this mode, data transmission may take place in either direction, but at a time data may be transmitted only in one direction. A computer may communicate with a terminal in this mode. It is not possible to transmit dat...