INTEL (Programmable Peripheral Interface). In previous lectures we have discussed how to interface I/O devices with the system bys. If an input device. The A is a programmable peripheral interface (PPI) device designed for use in Intel microcomputer systems. Its function is that of a general purposes I/O. Programmable Peripheral Interface. (Dated: pre). Features; Pinout; Block diagram; BSR mode; I/O mode; Mode 1; Mode 2.

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Mode O Basic Functional Definitions: The two modes are selected on the basis of the value present at 8255 programmable peripheral interface D 7 bit of the control word register. As an example, consider an input device connected to at port A.

Data is transmitted or received by the buffer upon execution of input or output instructions by the CPU. Since the two halves of port C are independent, they may be used such that one-half is initialized as 8255 programmable peripheral interface input port while the other half is initialized as an output port.

Input and Output data are latched. 8255 programmable peripheral interface is an active-low signal, i. Acknowledgement and handshaking signals 8255 programmable peripheral interface provided to maintain proper data flow and synchronisation between the data transmitter and receiver.

The inputs are not latched because the CPU only has to read their current values, then store the data in a CPU register or memory if it needs to be referenced at a later time. Port A can be used for bidirectional handshake data transfer.

Outputs are not latched. The Control Word Register can only be written into. From Wikipedia, the free encyclopedia. When we wish to use port A or port B for handshake strobed input or output operation, we initialise that port 8255 programmable peripheral interface mode 1 port A and port B can be initilalised to operate in different modes, i. The A contains three 8-bit ports AB, and C. In this mode, the may be used to extend the system bus to a slave microprocessor or to transfer data bytes to and from a floppy disk controller.


The ‘s outputs are latched to hold the last data written to them. When the A is programmed to operate in mode 1 or mode 2, control signals are provided that can used as interrupt request input to the CPU.

8255A – Programmable Peripheral Interface

The function of this 8255 programmable peripheral interface is to manage all of the Internal and External transfers of both Data and Control or Status words. For example, if port B and upper port C have to be initialized as input ports and lower port C and port A as output ports all in mode The functional configuration of 8255 programmable peripheral interface A is programmed by the systems software so that normally no external logic is necessary to interface peripheral devices or structures.

The Input signals, in conjunction with the RD and WR Inputs, controls the selection of one of the three ports or the control word registers. During the execution of the systems program any of the other modes may be selected using a single output Instruction. Two 8-bit ports and two 4-bit port Any port can be input or output. Input Control Signal Definition.

If from the 8255 programmable peripheral interface operation, port A is initialized as an output port and if is not reset before using the current configuration, then there is a possibility 8255 programmable peripheral interface damage of either the input device connected or or both, periphsral both and the device connected will be sending out data.


All Mask flip-flops are automatically peripherak during mode selection and device reset. Read operation of the Control Word Register is allowed.

The functional configuration of each port is programmed by the systems software. So, without latching, the outputs would become invalid as soon as the write cycle finishes.

The functionality of the 8255 programmable peripheral interface now mostly embedded in larger VLSI processing chips 8255 programmable peripheral interface a sub-function. Mode 1 Basic Functional Definitions: Some of the pins of port C function as handshake lines. The 5-bit control port Port C is used for control and status for the 8-bit,bi-directional bus port Port A. This feature reduces software requirements in Control-based applications.

Used in Group A only. Interrupt logic is supported.

Intel A Programmable Peripheral Interface

Views Read Edit View history. 8255 programmable peripheral interface instance; Group B can be programmed in Mode 0 to monitor simple switch closing or display computational results, Group A could be programmed in Mode 1 to monitor a keyboard or tape reader on an interrupt-driven basis. They are normally connected to the least significant bits of the address bus A0 and A1.

This mode is selected when D 7 bit of the Control Word Register 8255 programmable peripheral interface 1. Address lines A 1 and A 0 allow to access a data register for each port or a control register, as listed below:. 8255 programmable peripheral interface is required because the data only stays on the bus for one cycle. Retrieved from ” https: Mode 2 — Bi-Directional Bus.

This allows a single A to service a variety of peripheral devices with a simple software maintenance routine.