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Serial And Parallel Io 8251 And 8255 |LINK|


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. The 8255 provides 24 parallel input/output lines with a variety of programmable operating modes.




Serial And Parallel Io 8251 And 8255


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The 8255 gives a CPU or digital system access to programmable parallel I/O.[9]The 8255 has 24 input/output pins.[10] These are divided into three 8-bit ports (A, B, C).[11] Port A and port B can be used as 8-bit input/output ports. Port C can be used as an 8-bit input/output port or as two 4-bit input/output ports or to produce handshake signals for ports A and B.


We selected the Intel 8088 microprocessor because it has relatively higher execution speed, larger memory size, and additional instructions, which provides students with a practical knowledge of microcontroller technology. The IBM personal computer, which came out in mid-1981, was one of the earliest microcomputers to utilize a 16-bit microprocessor, the 8088, as its central processing unit (Triebel & Singh 1997). Through the construction process, students gain knowledge and experience in circuit design, wire-wrapping and soldering techniques, board design and parts layout, static and dynamic testing, programming, use of test equipment for analysis and troubleshooting, and data acquisition. Upon completion of the project, the student will have constructed a fully functional single board microcomputer with a 64K memory, a printer port, two serial ports, an analog-to-digital converter, and over 28 parallel input/output (I/O) lines. The project is organized around the following 12 steps:


The I/O decoder is installed in this exercise. The 8253/54 PIT (programmable interval timer), which is used to generate the timing signals to the peripheral I/O devices is installed. In the PC there is a single clock used to synchronize activities of all peripherals chips connected to the CPU. The clock, which has the highest frequency in the system, belongs to the 80x86 CPU Family. There are functions within the PC that require a clock with a lower frequency. The 8253 is used to drop the frequency to the desired level for various applications such as the beep a sound in the PC (Mazidi & Mazidi, 1993). The 74LS138 is a 3-to-8 decoder used to decode signals on the high-level address bus and select the proper I/O device for the microprocessor to access. It does this by taking the high level address and converting it to one of 8 inverting outputs connected to the chip select on each I/O device in the circuit. The 8253 is used as a baud rate generator. It sends the proper frequency square wave to the 8251A to make it a 9600 baud serial port. The circuits are wired and checked electrically and then a program is loaded into the EEPROM and the computer is started. The OUT pin is tested with an oscilloscope to be certain that the output frequency is 500 KHz.


The parallel I/O circuit is installed in this part of the project. The 8255 chip is a widely used I/O chip. It is designed for both memory-mapped and peripheral I/O. The 8255 is in a 40-pin DIP chip arrangement. It has three separately accessible ports, A, B, and C, this makes it much more economical than the 74LS244 and 74LS373 for I/O ports (Mazidi, Mazidi 1993). These ports can be programmed for either input or output and are used to interface the 8088 with different devices. Two 8255A chips are used in this computer. One is used as the printer interface and one is used to handle all other parallel I/O activities. The circuit is constructed and tested electrically without any chips installed; then, with all of the chips installed. A static test is done by putting a logic probe on the RESET pin of the 8255A and pressing the system reset button. When the button is pressed, the pin should go from logical 0 to logical 1. When the button is released, the pin should go from 1 back to 0. A test program is then loaded into EEPROM that configures the parallel ports and sends all 0?s and then all 1?s to them. The circuit is correct when a continuous ON-OFF-ON-OFF pattern is read at each bit of each port.


The primary serial I/O port is installed and tested in this section of the project. Serial communication in microcomputer circuits is discussed. This computer uses the 8251A Universal Synchronous/Asynchronous Receiver-Transmitter (USART) to handle serial communication. The 8251A is essentially a parallel-to-serial/serial-to-parallel converter that can be in either asynchronous or synchronous environments. It is programmable to fit a wide range of related applications (Goody, 1993). The USART is connected to the data bus where it takes an 8-bit data word and transmits it one bit at a time over a single wire at a predetermined clock speed called a baud rate. It receives data over a single wire, converting it back into 8-bit words for transmission over the data bus. The 8251A interface is interrupt driven so that the 8251A and the 8088 only talk when there is actual data to be transmitted or received. First, the circuit is wired and tested electrically. The MONITOR program is then loaded into the EEPROM and the computer is connected to a personal computer via serial ports for testing. The microcomputer is switched on and some characters are typed on the PC keyboard. If the keys are echoed by the microcomputer, the program and the circuit are operating properly. Figure 7 displays the serial I/O circuit.


The simple I/O interfacing method is discussed. The auxiliary parallel I/O circuit and the LED display are installed. The simple I/O method of interfacing calls for all input and output tohappen at specific times in the execution of a program as determined by software and not hardware interrupts. First, the LEDs and limiting resistors are installed. Then the DIP switchesare installed along with the pull up resistors. The LED portion of the circuit is wired to the 74LS240 and the DIP switches are wired to the parallel port A of the 8255. The connections are checked electrically and then the monitor program is used to send configuration information to the 8255 and sample data is inputted and outputted using the switches and LEDs. Figure 8 illustrates the parallel I/O circuit.


One computer that I don't see in your collection is the XOR CP/M computer that I found in a basement. I have the manuals for it and the full schematics (wow) and this one is dated around 1982. I have it connected to an ADDS Regent 25 terminal with a null modem rs232 cable (9600 baud) . There is also a parallel port on the back and another serial port. This one has 2 8" floppy drives, and I bought the last box of 8" floppies I could find in town ! (I think the store owner was glad to see them go...) I believe these computers were sold as a kit and you could pick components that you wanted. I have included a bad picture of the guts.


1. Programmable peripheral input-output port is another name fora) serial input-output portb) parallel input-output portc) serial input portd) parallel output portView AnswerAnswer: bExplanation: The parallel input-output port chip 8255 is also known as programmable peripheral input-output port. var adpushup = window.adpushup = window.adpushup ; adpushup.que = adpushup.que []; adpushup.que.push(function() adpushup.triggerAd("9f8aa9b5-2c42-4296-896e-70772ed1db59"); ); 2. Port C of 8255 can function independently asa) input portb) output portc) either input or output portsd) both input and output portsView AnswerAnswer: cExplanation: Port C can function independently either as input or as output ports.3. All the functions of the ports of 8255 are achieved by programming the bits of an internal register calleda) data bus controlb) read logic controlc) control word registerd) none of the mentionedView AnswerAnswer: cExplanation: By programming the bits of control word register, the operations of the ports are specified. Subscribe Now: Microprocessor Newsletter Important Subjects Newsletters advertisement var adpushup = window.adpushup ; adpushup.que = adpushup.que []; adpushup.que.push(function () { if (adpushup.config.platform === "MOBILE") adpushup.triggerAd("e5da93a0-b61a-4789-96be-a57ebec165b0"); else if ((window.outerWidth


8255 PPI and 8251 USART are peripheral controller chips designed to simplify I/O hardware design by incorporating all the logic for parallel (in case of 8255) or serial (in case of 8251) ports in one single package. These two chips need to be initialized for them to be used. But data transfer is controlled by CPU.


The RAM BIOS includes code to drive a serial port, though no serial portis present on my MBC. There is a 20-pin connector on the motherboard besidethe 8251; this corresponds to the serial port, which appears to consistof a daughterboard plugged into this connector.


This implements functions 0-3 of the standard INT 14h (serial) API. It only supports one serial port, so the value in DX (selecting which port to use) is ignored. Also, the "modem status" returned by AH=3 is largely fictitious, as the 8251 doesn't return many of the required signals.


8086 Operating at 4.77MHz.EEPROM: 32k word. Expandable up to 128k word.RAM: 32k word. Expandable to 128k words with Battery backup.24 I/O lines are using one number of 8255.Three 16bit Timer/ Counters using 8253.RS232 serial port using 8251 with level shifting.6 Digits of 7 segment displays.Keyboard with 24 high performance rugged and reliable keys.Monitor program with all the functions of the standard kit.Mounted in a sleek and eye catching wooden cabinet.Foolproof Battery backup for RAM.Microprocessor supervisory watchdog timer.Power supply:Specifications: Input 220V AC +/-10%,Output Voltage 5V, 1.2A; +12V, 0.75A; -12V, 0.75AWith short circuit and overload protection.


8086 operating at 4.77MHz.EPROM: 32k word. Expandable up to 256k words.RAM: 32k word. Expandable to 128k words with Battery backup.User Interaction:PC keyboard (101 keys) for program entry.Graphical LCD with 8 lines X 21 characters.Built in single line Assembler and Disassembler.Powerful program development facilities using GUI features.RS232 serial port using 8251 with level shifting.48 I/O lines using two 8255s.Three channels of 16bit Timer / Counters using 8253 with onboard clock generating facility.Interrupt Controller using 8259A.Onboard Interrupt study facility using Push Button switches.Onboard facility of 64k Byte EEPROM to store user programs with file management.Buffered Bus lines are terminated in three sets of 50 pin FRC headers.Centronics compatible printer port.Independent serial port for connecting with the computer for program development.Built in Self Diagnostic Facilities:Microprocessor health and performance.Memory testing.Peripheral testing facilities for 8255,8253 and 8259A.Power supply monitoring.Facility to indicate diagnostic results in the display.Facility to test and analyze serial port of the trainer.


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