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IO Interfaces and Bus Standards
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Interface circuits
• Consists of the cktry required to connect an i/o device to a computer.
• On one side we have data bus signals for address, data and control.
• On the other side we have a data path with its associated control to transfer data between the interface and the i/o device. This side is called port.– Parallel port– Serial port
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Functions of I/O interface ckt
• Provides a storage buffer for at least one word of data• Contains status flags that can be accessed by the
processor to determine whether the buffer is full or empty
• Contains address decoding cktry to determine when it is being addressed by the processor.
• Generates the appropriate timing signals required by the bus control scheme.
• Performs any format conversion that may be necessary to transfer data between the bus and the i/o device.
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Parallel port
• Multiple data path is used.
• Short distance
• Higher speed
• Usually a parallel port transfers a byte at one time.
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Input Interface ckt• Any input interface must
use three state logic device.
• Slave ready is set when either read status or read data is present.
• Any read operation is performed at master ready signal active.
• LSB address bit is used to identify the status read or data read.
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Output interface ckt• Output is latched• A0 is used to select either
status or data.• Handshake signals are
generated: idle, valid
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Combined Input/Output ckt
• A0, A1 2 bits are used to select status or data registers
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