Rockwell 6522 VIA

The 6522 Versatile Interface Adapter (VIA) was an integrated circuit made by MOS Technology, as well as second sources including Rockwell and Synertek. It served as a I/O port controller for the 6502 family of microprocessors, providing the parallel I/O capabilities of the PIA as well as timers and a shift register for serial communications. The 6522 was very popular in computers of the 1980s, particularly Commodore's machines, and was also a central part of the design of the Apple Macintosh. Image File history File links Download high resolution version (1408x512, 202 KB) Rockwell 6522 Versatile Interface Adapter in a 40-pin plastic DIL package. ... Image File history File links Download high resolution version (1408x512, 202 KB) Rockwell 6522 Versatile Interface Adapter in a 40-pin plastic DIL package. ... An integrated circuit (IC) is a thin chip consisting of at least two interconnected semiconductor devices, mainly transistors, as well as passive components like resistors. ... MOS Technology, Inc. ... Rockwell can refer to: Rockwell International - a defense company in the United States Rockwell Automation - an industrial automation company that descended from Rockwell International Rockwell Collins - a communications and aviation electronics company that also descended from Rockwell International Willard Rockwell - businessman who helped shape and name what became Rockwell International... Memory-mapped I/O (MMIO) and port I/O (also called port-mapped I/O or PMIO) are two complementary methods of performing input/output between the CPU and I/O devices in a computer. ... The MOS Technology 6502 is an 8-bit microprocessor designed by MOS Technology in 1975. ... The Peripheral Interface Adapter (PIA) is a peripheral integrated circuit providing parallel I/O interfacing capability for microprocessor systems. ... A timer is a specialized type of clock. ... In digital circuits a shift register is a group of registers set up in a linear fashion which have their inputs and outputs connected together in such a way that the data is shifted down the line when the circuit is activated. ... // Events and trends The 1980s marked an abrupt shift towards more conservative lifestyles after the momentous cultural revolutions which took place in the 1960s and 1970s and the definition of the AIDS virus in 1981. ... Commodore is the commonly used name for Commodore International, an electronics company who was a major player in the 1980s home computer field. ... The box for Mac OS X v10. ...

Input/output ports

The VIA contains 20 I/O lines, which are organised into 2 8-bit bidirectional ports (or 16 general-purpose I/O lines) and 4 control lines (for handshaking and interrupt generation). The directions for all 16 general lines (PA0-7, PB0-7) can be programmed independently. The control lines can be programmed to generate an interrupt when activated (all four), latch the corresponding I/O port (CA1 and CB1), automatically generate handshaking signals for devices on the I/O ports, or output a plain High or Low signal. For the greeting habit, see handshake. ... In computer science, an interrupt is a signal from a device which typically results in a context switch: that is, the processor sets aside what its doing and does something else. ...

Timers

The VIA provides 2 16-bit timer/counters, which can be used in one-shot (monostable) mode, free-running (divider) mode or "pulse counting" mode, where the timer will monitor the 7th bit (PA6 or PB6) on its respective I/O port, and count how many state transitions pass by. Each timer can generate an interrupt when it reaches zero, and can also output square waves on the 8th bit of its respective I/O port (pin PA7 or PB7). A monostable multivibrator is an electronic circuit that has two states, only one of which is stable. ... A square wave is a kind of basic waveform. ...

Shift register

The VIA's shift register is bidirectional, 8 bits wide, and can run from either a timer-generated clock (from timer 2), the CPU clock, or an external source on line CB1. The serial input/output is on line CB2, and CB1 can also be programmed to output a bit clock for external devices.