Книга: Introduction to Microprocessors and Microcontrollers

Input/output circuits

The signal on the data bus has only a very low power level and to be of use it must be amplified.

The first response was to put a series of amplifiers; one on the end of each of the connections on the data bus but this was soon superseded by a more sophisticated chip with more facilities. For example, if we wanted to send a signal to a printer at 1 ms intervals it would not be sensible to tie up the main processor with counting out these time intervals. It would be much better to tell the output chip to do its own timing and thus release the microprocessor for more important jobs.

The output devices have become quite complex and now go under a variety of names:

I/O controller – input/output controller

PIA – programmable interface adapter

VIA – versatile interface adapter

PIO – programmable input/output

PPI – programmable peripheral interface

…and many others.

Whatever name is given to the device, they are basically the same and are essential to any microprocessor-based system. An improved basic system is shown in Figure 7.5.

Figure 7.5 An input/output chip has been added

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