INTEL 8255A PDF

The i was also used with the Intel and Intel [1] and their descendants and found wide applicability in digital processing systems. It was later cloned by other manufacturers. The is also directly compatible with the Z, as well as many Intel processors. Data is transmitted or received by the buffer upon execution of input or output instructions by the CPU. Control words and status informa-tion are also transferred through the data bus buffer. CS Chip Select.

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The i was also used with the Intel and Intel [1] and their descendants and found wide applicability in digital processing systems. It was later cloned by other manufacturers. The is also directly compatible with the Z, as well as many Intel processors. Data is transmitted or received by the buffer upon execution of input or output instructions by the CPU.

Control words and status informa-tion are also transferred through the data bus buffer. CS Chip Select. A "low" on this input pin enables the communcation between the and the CPU. RD Read. A "low" on this input pin enables to send the data or status information to the CPU on the data bus.

In essence, it allows the CPU to "read from" the WR Write. A "low" on this input pin enables the CPU to write data or control words into the These input signals, in conjunction with the RD and WR inputs, control the selection of one of the three ports or the control word register. They are normally connected to the least significant bits of the address bus A0 and A1. A "high" on this input initializes the control register to 9Bh and all ports A, B, C are set to the input mode.

Group A and Group B Controls The functional configuration of each port is programmed by the systems software. In essence, the CPU "outputs" a control word to the The control word contains information such as "mode", "bit set", "bit reset", etc. All can be configured to a wide variety of functional characteristics by the system software but each has its own special features or "personality" to further enhance the power and flexibility of the Both "pull-up" and "pull-down" bus-hold devices are present on Port A.

This port can be divided into two 4-bit ports under the mode control. Each 4-bit port contains a 4-bit latch and it can be used for the control signal output and status signal inputs in conjunction with ports A and B. All information read from and written to the occurs via these 8 data lines.

CS Chip Select Input. If this line is a logical 0, the microprocessor can read and write to the RD Read Input Whenever this input line is a logical 0 and the RD input is a logical 0, the data outputs are enabled onto the system data bus.

WR Write Input Whenever this input line is a logical 0 and the CS input is a logical 0, data is written to the from the system data bus A0 - A1 Address Inputs The logical combination of these two input lines determines which internal register of the data is written to or read from. All peripheral ports are set to the input mode.

They can be connected to peripheral devices. If bit 7 of the control word is a logical 1 then the will be configured. If bit 7 of the control word is a logical 0 then each bit of the port C can be set or reset. Bit definitions of the control register to modify single bits of port C.

ISO 13486 PDF

8255A - Programmable Peripheral Interface

Mode selection bits, D2, D5, D6 are all 0 for mode 0 operation. 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. Input ports are buffered, not latched. Ports do not have handshake or interrupt capability. 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.

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INTEL 8255A PDF

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