The 6551 Asynchronous Communications Interface Adapter (ACIA) was an integrated circuit made by MOS Technology. It served as a companion UART chip for the widely popular 6502 microprocessor. Intended to implement RS-232, its specifications called for a maximum speed of 19,200 bits per second. It was used in the Commodore PET, Commodore Plus/4, Apple Computer's Super Serial Card for the Apple II family, Atari ST (where it is used for keyboard, mouse and MIDI support) and possibly other lesser-known computers. Integrated circuit showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window showing the integrated circuit inside. ... MOS Technology, Inc. ... A UART or universal asynchronous receiver-transmitter is a piece of computer hardware that translates between parallel bits of data and serial bits. ... The MOS Technology 6502 is an 8-bit microprocessor that was designed by Chuck Peddle for MOS Technology in 1975. ... A microprocessor (sometimes abbreviated µP) is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ... RS-232 (also referred to as EIA RS-232C or V.24) is a standard for serial binary data interchange between a DTE (Data terminal equipment) and a DCE (Data communication equipment). ... In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ... The PET (Personal Electronic Transactor) was a home-/personal computer produced by Commodore starting in the late 1970s. ... Commodore Plus/4. ... Apple Inc. ... Apple II serial cards primarily used the serial RS-232 protocol. ... The 1977 Apple II, complete with integrated keyboard, color graphics, sound, a plastic case and eight expansion slots. ... The Atari 520ST Atari 1040STF with SC1224 color monitor The Atari ST is a home/personal computer that was commercially popular from 1985 to the early 1990s. ...

Commodore International omitted the 6551 from the popular VIC-20, C64, and C128 home computers. Instead, these systems implemented a bit-banging UART via KERNAL routines. This RS-232 implementation was not reliable over 1200 bit/s (see errata comments in the 6526 article), forcing some programmers of terminal programs to write carefully calibrated custom serial routines. The popular terminal program NovaTerm was able to achieve 4800 bit/s on the C64, and DesTerm achieved 9600 bit/s on the C128. Several other terminal programs achieved 2400 bit/s. Commodore, the commonly used name for Commodore International, was an American electronics company based in West Chester, Pennsylvania which was a vital player in the home/personal computer field in the 1980s. ... The VIC-20 (Germany: VC-20; Japan: VIC-1001) is an 8-bit home computer. ... The Commodore 64 is the best selling single personal computer model of all time. ... The Commodore 128 (C128, CBM 128, C=128) home/personal computer was Commodore Business Machines (CBM)s last commercially released 8-bit machine. ... Children playing on a Amstrad CPC 464 in the 1980s. ... Bit-banging is an technique to communicate on a serial bus without the use of an UART in embedded systems. ... The KERNAL is Commodores name for the ROM-resident operating system core in its 8-bit home computers; from the original PET of 1977, via the extended, but strongly related, versions used in its successors; the VIC-20, C64, Plus/4, C16, and C128. ... Pin configuration of the 6526 CIA The 6526/8520 Complex Interface Adapter (CIA) was an integrated circuit made by MOS Technology. ... A terminal emulator, terminal application, term, or tty for short, is a program that emulates a dumb video terminal within some other display architecture. ...

Several companies, including Dr. Evil Labs and Creative Micro Designs, marketed an add-on cartridge containing a 6551 and an industry-standard RS-232 port to allow the C64 and 128 to use high-speed modems from companies such as U.S. Robotics and Hayes Communications. The Dr. Evil and CMD cartridges pushed the 6551 to a maximum speed of 38,400, and with a faster-still clock crystal, some end users reported getting 115,200 bit/s out of the chip. Creative Micro Designs (CMD) is a computer technologies company which today sells PCs and equipment, but which started out in 1987 selling self-designed hardware for the Commodore 64 and C128 8-bit computers. ... In various types of electronic equipment, a cartridge can refer one method of adding different functionality or content (e. ... U.S. Robotics (popularly nicknamed USR), based in Schaumburg, Illinois and founded in 1976, is a company that makes computer modems and related technologies. ... Hayes Communications was a U.S.-based manufacturer of modems. ...

Variants

The Rockwell 65C52 combines two 6551s on a chip. Conexant is a publicly listed NASDAQ: CNXT semiconductor company, which was formerly the semiconductor division of Rockwell International. ...

Interface chips from MOS Technology and second source/clone vendors

6520 PIA ● 6522 VIA ● 6523 TIA ● 6525 TPI ● 6526 CIA ● 6529 SPI ● 6530 RRIOT ● 6532 RIOT ● 6551 ACIA Image File history File links MOS_Technology. ... 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. ... Integrated circuit showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window showing the integrated circuit inside. ... 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. ... Pin configuration of the 6526 CIA The 6526/8520 Complex Interface Adapter (CIA) was an integrated circuit made by MOS Technology. ... The 6529 Single Port Interface (SPI aka PIO) was an integrated circuit made by MOS Technology. ... The 6530 ROM-RAM-I/O-Timer (RRIOT) was an integrated circuit made by MOS Technology, as well as second sources such as Rockwell. ... MOS 6532 RIOT is integrated circuit which contains 128 bytes of RAM, timer and two 8 bit I/O gate. ...

Novaterm 9.6 on a Commodore 64 or 128, can achieve a maximum rate of 9600bps on the user port, using an EZ-232 interface, designed by Jim Brain.