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
Instruction set of 8086 : The 8086/8088 instructions are categorized into the following major types. This section describes the function of each of the instructions with approp

1. Write an assembly program that adds the elements in the odd indices of the following array. Use LOOP. What is the final value in the register? array1 DWORD 10, 20, 30, 40, 50, 6

Pin functions for the minimum mode operation of 8086 are following: 1) M/I/O -Memory/IO: This is a status line logically equivalent to S2 in maximum mode. When it is low, it

Write a program to mask bits D3D2D1D0 and to set bits D5D4 and to invert bits D7D6 of ax register

You have to write a subroutine (assembly language code using NASM) for the following equation.

move a byte string ,16 bytes long from the offset 0200H to 0300H in the segment 7000H

write a program assembly language for adding two 3*3 matrix

1- Write an assembly program that:   a- Defines an array of 10 (word type)elements;   b- Finds out the number of negative elements   c- Calculate the summation of the posi


Program is written but has errors returning values from the procedure.