8255 programmable peripheral interface-microprocessor, Assembly Language

8255 Programmable Peripheral Interface

Intel's 8255 A programmable peripheral interface provides a nice instance of a parallel  interface. As shown the interface have a control register and 3 separately addressable ports, denoted from A, B, and C. Whether or not an 8255A is being accessed is determined by the signal on the CS pin and the direction of the access is according to the WR and RD signals. Which of the 4 registers is being addressed is determined by the signals applied to the pins A0 and A1. So, the lowest port address assigned to an 8255 A might be divisible by 4. A review of the 8255 A's addressing is:

A1        A0        RD       WR      CS        Transfer Description

0          0          0          1          0          Port A to data bus

0          1          0          1          0          Port B to data bus

1          0          0          1          0          Port C to data bus

0          0          1          0          0          Data bus to port A

0          1          1          0          0          Data bus to port B

1          0          1          0          0          Data bus to port C

1          1          1          0          0          Data bus to control register if D7= 1; if D7=0 input from the data bus is treated as a Set/Reset instruction

x          x          x          x          1          D7-D0 go to high-impedance state

1          1          0          1          0          Illegal combination

x          x          1          1          0          D7-D0 go to high-impedance state

Where 0 is low and 1 is high

Because the bits in port C are sometimes utilized as control bits, the 8255 A is designed so that they may be output to separately by using a Reset/set instruction. When the 8255 A receives a byte that is directed to its control register, it checked data bit 7.If this bit is one, the data are transferred to the control register, but if it is zero, the data retreated as a Reset/set instruction and is utilized to clear or set the port C it denoted by the instruction. Bits 3-1 gives the bit number of the bit to be changed and bit 0 denote whether it is to be cleared or set. The remaining bits are not useful.

535_8255.jpg

The bits in the 3 ports are attached to pins that can be linked to the I/O device. These bits are divided into groups A & B, with group A consisting of the bits in port A and the 4 MSBs of port C and group b consisting of port B and the 4 LSBs of port C. the use of each of the 2 groups is controlled by the mode connected with it. Group A is connected with 1 of 3 modes, mode zero, mode one, and mode two, and group B with 1 of 2 modes, mode 0 and mode 1.

 

Posted Date: 10/10/2012 6:51:27 AM | Location : United States







Related Discussions:- 8255 programmable peripheral interface-microprocessor, Assignment Help, Ask Question on 8255 programmable peripheral interface-microprocessor, Get Answer, Expert's Help, 8255 programmable peripheral interface-microprocessor Discussions

Write discussion on 8255 programmable peripheral interface-microprocessor
Your posts are moderated
Related Questions
DAS: Decimal Adjust after Subtraction:- This instruction converts the result of subtraction operation of 2 packed BCD numbers to a valid BCD number. The subtraction operation has

1 st Generation Microprocessor : At the end of the 70s a group of engineers developed a chip is able to processing data. This chip was called processor chip. Big processors w

to separate positive and negative numbers

Assembly Code for Reading Flow & Generating Serial Output The timer is timer 1 is set for the baud rate 9600, as the crystal used is of 11.0592 Hz.  Then the timer 1 is starte

Ask 2. Exchange higher byte of AX and higher byte of BX registers by using memory location 0160 in between the transfer. Then stores AX and BX registers onto memory location 0174 o

Print Media Advertising (PMA) has been providing a contract to market Buzz Cola via newspaper ads in a main southern newspaper. Full-page ads in the weekday editions (Monday throug

SEG : Segment of a Label:- The SEG operator is which is used to decide the segment address of the, variable, label or procedure and substitutes the segment base address in plac

Why is the capability to relocate processes desirable?

Pin diagram of 8088 : The pin diagram of 8088 is shown in given figure. Most of the 8088 pins and their functions are exactly similar to the corresponding pins of 8086.  Hence

Write a M68000 assembly language subroutine MULSUM that takes an array named A containing n bytes of positive numbers, and fills two arrays, array B containing n