Microprocessor Interfacing

A microprocessor is a device that incorporates almost all of the functions of a computer’s central processing unit (CPU) on a single integrated circuit (IC, or microchip).

The first devised microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal (BCD) arithmetic on 4-bit words. Other embedded are users of 4-bit and 8-bit microprocessors, such as terminals, printers, various kinds of automation etc., followed soon after. Presently commonly used 8-bit microprocessors with 16-bit addressing also led to the first general-purpose microcomputers from the mid-1970s on.

During the year 1960s, computer processors were often constructed out of small and medium-scale ICs containing from tens to a few hundred transistors. The integration is that of a CPU onto a single chip greatly reduced the cost of processing power. From this poor beginning it continued increasing in the microprocessor capacity having rendered other forms of computers almost completely obsolete, with one or more microprocessors used in everything from the smallest embedded systems and handheld devices to the largest mainframes and supercomputers.

Peripheral Interface Adapter

The Peripheral Adapter is a peripheral integrated circuit providing parallel I/O interfacing capability for microprocessor systems. Common PIAs contains the Motorola MC6820 and MC6821, and the MOS Technology MCS6520, all of which is functionally identical but have slightly different electrical characteristics. The PIA is the most commonly packaged in a 40 pin DIP package.

The PIA are designed for glue less connection to the Motorola 6800 style bus, and provides 20 I/O lines, which are organized into 2 8-bit bidirectional ports (or 16 general-purpose I/O lines) and 4 control lines (for handshaking and interrupt generation). The directions of all 16 general lines (PA0-7, PB0-7) can be programmed independently. The controls can be programmed to generate interrupts, automatically generate handshaking signals for devices on the I/O ports, or output a plain high or low signal.