Pin configuration of the 6526 CIA

The 6526/8520 Complex Interface Adapter (CIA) was an integrated circuit made by MOS Technology. It served as a I/O port controller for the 6502 family of microprocessors, providing for parallel and serial I/O capabilities as well as timers and a Time-of-Day (TOD) clock. The circuit's most prominent use was in the Commodore 64, Commodore 128, and Amiga home computers, each of which included two CIA chips. Optical Microscope image of an integrated circuit showing defects in the aluminium layer deposition. ... MOS Technology, Inc. ... 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. ... In computing, a parallel port is an interface from a computer system where data is transferred in or out in parallel, that is, on more than one wire. ... This article needs to be cleaned up to conform to a higher standard of quality. ... A Programmable Interval Timer (PIC) provides one or more counters which trigger an interrupt when they reach their programmed count. ... Commodore 64 (1982) The Commodore 64 (C64, CBM 64/CBM64, C=64) is a home computer with 64 kilobytes of RAM that was popular in the 1980s. ... The Commodore 128 is a home/personal computer, also known as the C128. ... The Amiga is a family of home/personal computers originally developed by Amiga Corporation as an advanced game console. ... The home computer is a consumer-friendly word for the second generation of microcomputers (the technical term that was previously used), entering the market in 1977 and becoming common during the 1980s. ...

Parallel I/O

The CIA had two 8-bit bidirectional parallel I/O ports. Each port had a corresponding Data Direction Register, which allowed each data line to be individually set to input or output mode. 8-bit refers to the number of bits used in the data bus of a computer. ...

Serial I/O

An internal bidirectional 8-bit shift register enabled the CIA to handle serial I/O. The chip could accept serial input clocked from an external source, and could send serial output clocked with one of the built-in programmable timers. An IRQ was generated whenever an 8-bit serial transfer has completed. 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. ... In computer science, an interrupt is a signal from a device which typically results in a (register) context switch: that is, the processor sets aside what its doing and does something else. ...

Handshaking

Two dedicated control lines (/FLAG and /PC) were implemented to allow coordination between multiple CIA chips.

Interval timers

Two programmable interval timers were available. Each timer consisted of a 16-bit read-only presettable down counter and a corresponding 16-bit write-only latch. Whenever a timer was started, the timer's latch was automatically copied into its counter, and the counter would then decrement with each clock cycle until underflow, at which an IRQ would be generated. The timer could run in either "one-shot" mode, halting after the first IRQ, or "continuous" mode, reloading the latch value again and starting the timer cycle anew. In addition to generating IRQs, the timer output could also be gated to the second I/O port. In computer science, 16-bit is an adjective used to describe integers that are at most two bytes wide, or to describe CPU architectures based on registers, address buses, or data buses of that size. ... Read-only memory (ROM) is used as a storage medium in computers. ... This article is about the term counter used in electronics and computing. ... Write Only Memory (WOM) is the logical converse of Read Only Memory. ... A latch is a type of door or window lock (device). ...

Time-of-Day (TOD) Clock

A real-time clock was incorporated in the CIA. Accurate to a tenth of a second, it could be driven by either a 50 Hz or 60 Hz external signal, selected by a user-programmable register. This was to ensure compatibility with both NTSC and PAL systems. The clock operated in binary-coded decimal. Latching and halting behavior was implemented to prevent errors when reading or writing the clock. An "alarm" feature was also included, which allowed an IRQ to be generated whenever a certain time of day was reached. The 8520 revision, used in the Amiga, modified the time-of-day clock to be a 24-bit binary counter, replacing the BCD format of the 6526. NTSC is the analog television system in use in Korea, Japan, United States, Canada and certain other places, mostly in the Americas (see map). ... For other meanings of PAL see PAL (disambiguation). ... Binary-coded decimal (BCD) is, after character encodings, the most common way of encoding decimal digits in computing and in electronic systems. ... The Amiga is a family of home/personal computers originally developed by Amiga Corporation as an advanced game console. ...

Versions

The CIA was available in 1 MHz (6526) and 2 MHz (6526A) versions. The form factor was a JEDEC-standard 40-pin ceramic or plastic DIP. The 8520 CIA, with its modified time-of-day clock, was used in the Amiga computers. MegaHertz (MHz) is the name given to one million (106) Hertz, a measure of frequency. ... Form factor refers to the linear dimensions and configuration of a device as distinguished from other measures of size (for example Gigabytes; a measure of storage size): in computing, form factor is used to describe the size and format of PC motherboards (see AT, ATX, BTX), but also of hard... JEDEC stands for Joint Electron Device Engineering Council and is the semiconductor engineering standardization body of the Electronic Industries Alliance (EIA), a trade association that represents all areas of the electronics industry. ... The word ceramic is derived from the Greek word Κεραμεικος (the name of a suburb of Athens), and in its strictest sense refers to clay in all its forms. ... Plastic is a term that covers a range of synthetic or semisynthetic polymerization products. ... IC in a DIP14-Package In electronics, a Dual In-line Package (DIP), sometimes called a DIL package, is an electronic device package with a rectangular housing and a row of electrical connecting pins along each of two opposite sides, usually the longer sides of the rectangle. ... The Amiga is a family of home/personal computers originally developed by Amiga Corporation as an advanced game console. ...

External links

• MOS 6526 CIA datasheet (GIF format, zipped)
• MOS 6526 CIA datasheet (PDF format)

Interface chips from MOS Technology and second source/clone vendors

6520 PIA ● 6522 VIA ● 6526 CIA ● 6529 SPI ● 6530 RRIOT ● 6532 RIOT ● 6551 ACIA For more generic meanings of input/output port, see port (computing). ... Optical Microscope image of an integrated circuit showing defects in the aluminium layer deposition. ... MOS Technology, Inc. ... The Peripheral Interface Adapter (PIA) is a peripheral integrated circuit providing parallel I/O interfacing capability for microprocessor systems. ... 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. ... MOS 6532 RIOT is integrated circuit which contains 128 bytes of RAM, timer and two 8 bit I/O gate. ... The MOS 6551 Asynchronous Communications Interface Adapter was a simple UART chip produced by MOS Technology. ...