8255 DMA CONTROLLER PDF

It is designed by Intel to transfer data at the fastest rate. Then the microprocessor tri-states all the data bus, address bus, and control bus. These are the four individual channel DMA request inputs, which are used by the peripheral devices for using DMA services. When the fixed priority mode is selected, then DRQ 0 has the highest priority and DRQ 3 has the lowest priority among them. These are the active-low DMA acknowledge lines, which updates the requesting peripheral about the status of their request by the CPU.

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The Intel or i Programmable Peripheral Interface PPI chip was developed and manufactured by Intel in the first half of the s for the Intel microprocessor. The is a member of the MCS Family of chips, designed by Intel for use with their and microprocessors and their descendants. The functionality of the is now mostly embedded in larger VLSI processing chips as a sub-function.

All of these chips were originally available in a pin DIL package. Address lines A 1 and A 0 allow to access a data register for each port or a control register, as listed below:. It is an active-low signal, i. As an example, consider an input device connected to at port A. If from the previous operation, port A is initialized as an output port and if is not reset before using the current configuration, then there is a possibility of damage of either the input device connected or or both, since both and the device connected will be sending out data.

The two modes are selected on the basis of the value present at the D 7 bit of the control word register. Each line of port C PC 7 - PC 0 can be set or reset by writing a suitable value to the control word register. This mode is selected when D 7 bit of the Control Word Register is 1. 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 0 :. The two halves of port C can be either used together as an additional 8-bit port, or they can be used as individual 4-bit ports.

Since the two halves of port C are independent, they may be used such that one-half is initialized as an input port while the other half is initialized as an output port. The 's outputs are latched to hold the last data written to them. This is required because the data only stays on the bus for one cycle. So, without latching, the outputs would become invalid as soon as the write cycle finishes. 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.

If an input changes while the port is being read then the result may be indeterminate. When we wish to use port A or port B for handshake strobed input or output operation, we initialise that port in mode 1 port A and port B can be initialised to operate in different modes, i.

Some of the pins of port C function as handshake lines. For port B in this mode irrespective of whether is acting as an input port or output port , PC0, PC1 and PC2 pins function as handshake lines.

Only port A can be initialized in this mode. Port A can be used for bidirectional handshake data transfer. This means that data can be input or output on the same eight lines PA0 - PA7. 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. Acknowledgement and handshaking signals are provided to maintain proper data flow and synchronisation between the data transmitter and receiver.

From Wikipedia, the free encyclopedia. Two ports i. Interrupt logic is supported. Input and Output data are latched. Microprocessor And Its Applications. New Age International. Retrieved 3 June Miller Freeman Publications. July Renesas Electronics. Retrieved 26 July Brady Communications Co. Reed Business Pub. Techmax Publication. Namespaces Article Talk. Views Read Edit View history.

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Intel 8255

We can program it according to the given condition. It can be used with almost any microprocessor. We can assign different ports as input or output functions. Port C is further divided into two 4-bit ports i.

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