In this format, the 8bit port address is carried on address bus a0 a7. The control words written to control register specify an io function for each i. The other thing i didnt like about the 8020 is that the labeling. For eg, if d0 d4 1, then lower port c and port a act as input. It has 24 io programmable pins like pa,pb,pc 38 pins. Control word format for 8255a electronics engineering. D0 or d1 or d3 or d4 are set, the corresponding ports act as input ports. The 8255 can be either memory mapped or io mapped in the system. If you like geeksforgeeks and would like to contribute, you can also write an article using contribute.
Adc interfacing with 8085 ppi 8255 8155 intel microprocessor block diagram. Programmable peripheral interface the 8255a is a general purpose programmable io device designed for use with intel microprocessors. Control word of 8255 port c lower pc 3pc 0 1 input, 0 output port b 1 input, 0 output mode selection 0 mode0, 1 mode1 port c upper pc 7pc 4 1 input, 0 output port a 1 input, 0 output mode selection 00 mode0, 01 mode1 1x mode 2 1 i o mode 0 bsr mode group b group a d 7 6 5 4 3 2 1 0 engr 4862 microprocessors. The intel 8255a is a general purpose programmable io. Microprocessor 8255 programmable peripheral interface. Find the control word if pa out, pb in, pc0 pc3 in, and pc4pc7 out. Each of control blocks group a and group b accept commands from readwrite control logic, receives control words from the internal data bus and issue the proper commands to its associate ports. D0, d1, d3, d4 afor lore wer port c, port b, upper port c and port a respectively. These input signals work with rd, wr, and one of the control signal. The bit d7 of the control word determines either the io function of the bsr function. The 8255 programmable peripheral interface intel has developed several peripheral controller chips designed to support the 80x86 processor family. Figure 4 shows the control word format for both read and write operations. The control word contains information such as mode, bit set, bit reset, etc.
The control word format of the 8255 is shown in fig. Hi, control register is the register which tells the 8255 programmable peripheral extender that which port is at output mode and which is at input mode. Control word register cwr also tells 8255, the mode in which 8255 is going to be used. Programmable peripheral interface 8255 geeksforgeeks. When 8255 microprocessor is reset, it will clear the control word register contents, setting all the ports to input mode. Programmable peripheal interface, 8255a datasheet, 8255a circuit, 8255a data sheet. For the love of physics walter lewin may 16, 2011 duration. The first format is valid for io modes of operation, i. Function of pins pin function of pin d0d7 data bus these are bidirectional, tristate data bus lines are connected to the system data bus. Figure 6 shows the control word format for both read and write operations.
It consists of three 8bit bidirectional io ports 24io lines that can be configured to meet different system io needs. The contents of this register, called the control word, specify an io function for each port. What is the purpose of control word written to control. Requires insertion of wait states if used with a microprocessor using higher that an 8 mhz clock. Port a contains one 8bit output latchbuffer and one 8bit input.
This can be achieved by programming the bits of an internal register of 8255 called as control word register cwr. In io mode, the 8255 ports work as programmable io ports, while in bsr mode only port c pc0pc7 can be used to set or reset its individual port bits. The figure shows the control word format in the inputoutput mode. The internal block diagram of 8255 is shown in fig. The control word format of bsr mode is as shown in the figure below the pin of port c is selected using bit select bits b b b and set or reset is decided by bit sr the bsr mode affects only one bit of port c at a time. The pin that clears the control word register of 8255 when enabled is a clear b set c reset d clk answer.
Port c eight pins can be grouped into two 4bit as cuppercu and clower cl or used as individual the functions of these ports are defined by writing control word to the control register. The intel 8255 or i8255 programmable peripheral interface ppi chip was developed and. The contents of the control register are called the control word that specifies the input output functions of each port. These input signals, in conjunction with the and inputs, control the selection of one of the three ports or the control word registers. The 8255 is a member of the mcs85 family of chips, designed by intel for use with their 8085 and 8086 microprocessors and. As per the requirement of the programmer the control word is written into the control word register of 8255a. Each of the control blocks group a and group b accepts commands from the readwrite control logic, receives control words from the internal data bus and issues the proper commands to its. Part, manufacturer, description, pdf, samples, ordering.
Mode 0, 1 or 2 by sending a byte or control word to. What are the basic modes of operation of 8255, explain with the. Ppi 8255 interface with 8085 datasheet, cross reference, circuit and application notes in pdf format. If the most significant bit of control word or d7 is 1 then 8255 works in io mode else, if its value is 0 it works in bsr mode. Control word format figure 3 shows a register called the control register. The control word format of bsr mode is as shown in the figure below. D5, d6 are used for mode selection for group a upper port c and port a. A port is used to communicate between external io device and microprocessor. The format for the control word format for 8255a is shown in figure bellow. The 8255a is a general purpose programmable io device designed to transfer the data from io to interrupt io under certain conditions as required. D7 0 d4, d5, d6 not used d1, d2, d3 for selecting any particular line of port c d0 1 for set, 0 for reset to set pc7 line, cw would be 0 bsr mode 000 111 line 7 1 to set to set pc4 line cw 0 000 100 1 to reset pc4 line cw 0 000 100 0.
So from above control word format for 8255a diagram we can see the bit wise function of control word generation. Such a card allows you to do both digital input and output dio to your pc. This set of microprocessor multiple choice questions. Ppi 8255 is a general purpose programmable io device designed to interface the cpu with its outside world such as. Under the io mode of operation, further there are three modes of operation of 8255, so as to support different types.
You may do so in any reasonable manner, but not in. Mode selection bits, d2, d5, d6 are all 0 for mode 0 operation. The 8255 provides 24 parallel inputoutput lines with a variety of programmable operating modes. The control word register can be both written and read as shown in the address decode table in the pin descriptions. It is used to interface to the keyboard and a parallel printer port in pcs usually as part of an integrated chipset. View and download onkyo tx8255 instruction manual online. If 8255 control word is 94h,tell the chip port work mode. Please read this manual thoroughly before making connections and plugging in the unit. The intel 8255a is a general purpose programmable io device which is designed for use with all intel and most other microprocessors. Intel, alldatasheet, datasheet, datasheet search site for electronic components. When cpu wants to send data to slow peripheral device like printer, it will.
The intel 8255 or i8255 programmable peripheral interface ppi chip was developed and manufactured by intel in the first half of the 1970s for the intel 8080 microprocessor. Bsr mode when msb of the control register is zero0, 8255 works in bit setreset this only pc bit are used for set and reset. If port b and upper port c have to be initialised as input ports and lower port c and port a as ouput ports all in mode 0, what is the control word. The control word register can be both written and read as shown in the basic operation table. The contents of the control register are called the control word that specifies the input output.
Now we will see how can we tell microprocessor that which port of 8255 we use as input or output. The following are the control signals when ports a and b act as input ports under mode 1. When the control word is read, bit d7 will always be a logic 1, as this implies control word mode information. The three ports are defined in 3 modes which are controlled by control word in control register. The mode format for io as shown in figure the control word for both mode is same. Control word format control word format in inputoutput mode. En stereo receiver tx8255 instruction manual thank you for purchasing an onkyo stereo receiver. In order to promote public education and public safety, equal justice for all, a better informed citizenry, the rule of law, world trade and world peace, this legal document is hereby made available on a noncommercial basis, as it is the right of all humans to. Introduction the 8255 programmable peripheral interface ppi is a versatile and easy to construct circuit card the plugs into an available slot in your ibm pc. A simple schematic for interfacing the 8255 with 8085 processor is shown in fig. If reset pin is enabled then the control word register is cleared. Control word register thus one may have either three 8bit io ports or two 8bit and two 4bit ports from 8255. What are the basic modes of operation of 8255, explain. In essence, the cpu outputs a control word to the 8255.
This file is licensed under the creative commons attributionshare alike 3. Peripheralinterfacing of 8085 free 8085 microprocessor. They are normally connected to the least significant bits of the address bus a 0 and a 1. Stereo receiver tx8255 onkyo asia and oceania website. The blog talks about variety of topics on embedded system, 8085 microprocessor, 8051 microcontroller, arm architecture, c2000 architecture, c28x, avr and many many more. If you have any questions regarding this free computer science tutorials,short questions and answers,multiple choice questions and answersmcq sets,online testquiz,short study notes dont hesitate to contact us via facebook,or through our website. All of these ports can function independently either as input or as output ports.
What is the purpose of control word written to control register in 8255. The control word format, when 8255 is operated in io mode, is shown below. Etc2 93 ohm,alldatasheet, datasheet, datasheet search site for electronic components and semiconductors. The intent is to provide a complete io interface in one chip. They are used to transfer data and control word from microprocessor 8085 to 8255 or receive data or status word from 8255 to the 8085. This register can be accessed to write a control word when a0 and a1 are at logic 1, as mentioned. If msb of control word d7 is 1, ppi works in inputoutput mode.
For 8255 ppi to be operated in io mode, d7 bit must be 1. It consists of three 8bit bidirectional io ports 24io lines which can be configured as per the requirement. When 8255 microprocessor is reset, it will clear the control word register. For my setup, the 8255 was far more efficient in powering my speakerturntable combo.
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