8255 programmable peripheral interface-microprocessor, Assembly Language

Assignment Help:

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.

 


Related Discussions:- 8255 programmable peripheral interface-microprocessor

General data registers-microprocessor, General Data Registers Given fig...

General Data Registers Given figure indicate the register organization of 8086. The registers DX, CX, BX and AX are the general purpose 16-bit registers. AX is behaved as 16-bi

8088 timing system diagram-Microprocessor, 8088  Timing System Diagram ...

8088  Timing System Diagram The 8088 address/data  bus is divided  in 3 parts (a) the lower 8 address/data  bits, (b) the middle 8 address bits, and (c) the upper 4 status/

Port mapped or mapped input output, Port Mapped I/O or I/O Mapped I/O I...

Port Mapped I/O or I/O Mapped I/O I/O devices are mapped into a separate address space. This is generally accomplished by having a different set of signal lines to denote a mem

Program, Write a program to separate out positive and negative numbers from...

Write a program to separate out positive and negative numbers from a given series of 16-bit hexadecimal numbers.

Inc-arithmetic instruction-microprocessor, INC: Increment : - This instruct...

INC: Increment : - This instruction increments the contents of the particular memory or register location by the value 1. All the condition code flags are affected except the carry

ISBN CHECK, How do i convert a asci number to numerals?

How do i convert a asci number to numerals?

Flowchart for the sequence of 8251-microprocessor, Flowchart for the sequen...

Flowchart for the sequence of 8251 Whether the control, mode or sync character register is selected depends on the accessing sequence.  A flowchart of the sequencing is given i

LC-3 Program, Write an Lc-3 assembly language program to read in a sequence...

Write an Lc-3 assembly language program to read in a sequence of single-digit positive integers from the keyboard(one integer per line) until the sentinel value of 0 is reached and

8251 programmable/communication interface-microprocessor, 8251 Programmable...

8251 Programmable/Communication Interface As an instance of a serial interface device let us suppose Intel's 8251 A programmable communication interfaces. The 8251A is diagram

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd