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Processor & Device Communication
During the I/O operation, the I/O module must communicate with the processor and with the external device.
Processor communication involves the following -
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Command decoding : |
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The I/O module accepts command from the processor, typically sent as signals on control bus.
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Data : |
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Data are exchanged betweeen the processor and the I/O module over the data bus.
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Status Reporting : |
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Because peripherals are so slow, it is important to know the status of the I/O module. For example, if an I/O module is asked to send data to the processor(read), it may not be ready to do so because it is still working on the previous I/O command. This fact can be reported with a status signal. Common status signals are BUSY and READY.
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Address Recognition : |
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Just as each word of memory has an address, so thus each of the I/O devices. Thus an I/O module must recognize one unique address for each peripheral it controls.
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On the other hand, the I/O must be able to perform device communication. This communication involves command, status information and data.
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