From BeebWiki
Jump to: navigation, search

I/O Interfaces

  • 1Mhz Bus
  Expandable port for adding devices directly to the system bus.
  Devices can be daisy chained if properly designed.
  Used for two purposes, each with its own named memory-mapped area.
  FRED is used for hard discs and user peripherals.
  Addresses were assigned by Acorn so they wouldn't clash.
  Includes a 'paging register' for JIM.
  JIM is used for RAM discs and memory extensions.
  This makes the RAM available in a 256 byte 'window'.
  A famous example is the Challenger which also adds a floppy drive.
  • Disk Drive interface
  A standard Shugart disc drive connector supporting 2 floppy drives.
  Originally used with 5.25" floppy discs.
  Recent 3.5" PC floppy drives can be used, with patched software.
  Needs custom cable if using two such drives.
  Driven by an Intel 8271, or Western Digital 1770 on B+.
  Some third party expansion boards appeared with varying controller chips.
  • User Port
  Used for AMX Mouse, handheld scanner, robotic control and hobby projects.
  Convenient source of logical outputs/inputs, simple to use.
  Driven by B side of User VIA.
  • Tube
  A custom interface to permit the BBC range of machines access to an additional processor.
  Proprietary design and registered trademark of Acorn.
  The processor bus leads out to a custom chip on the second processor board.
  The chip provids four × 2-way data channels.
  On power up the second processor takes control of the BBC Micro which does all the I/O.
  The 2nd proc. only needs the CPU, RAM, a tiny ROM and the Tube ULA.
  Most of the work lies in the Tube protocol governing the channels.
  • Printer Port
  Allows the BBC Micro to drive a Centronics-type parallel printer.
  Driven by the A side of the User VIA, through a one-way buffer.
  The operating system had extensive printer support.
  • TV UHF
  Colour TV signal for connecting to a TV's aerial socket.
  Generated by an off-the-shelf module with a built-in socket.
  Tuned to channel 36 by default.
  • RGB
  Separate TTL outputs for a dedicated monitor.
  Such as the famous Microvitec Cub.
  With sync signals on a separate pin.
  • Video Out
  Composite PAL video presented on a BNC female connector.
  Monochrome by default, could be made colour with a modification or jumper.
  • Econet
  Acorn's proprietary networking solution, using cheap twisted pair cable.
  Driven by a 68B54 ADLC chip.
  The network has to provide a clock before the BBC Micro can use it.
  Econet networks have a bus topology, with bridges allowed between networks.
  Eventually, Acorn developed solutions to bridge Econet with Ethernet.
  • Cartridge Port(s)
  Electron and Master Only.
  Used to insert ROMs with less wear and tear.
  Also for hardware expansion such as disc drives.
  • SCSI
  Internal addon board used for the Master AIV.
  • Modem connector
  The Master series provided for an internal modem.
  • RS423
  The serial port which can communicate over longer cables than RS232.
  Voltage compatible with RS232 to connect to external modems, etc.
  Driven by a 6850 ACIA, through the Serial ULA.
  • Cassette port
  Can load and save tapes in CUTS format and an Acorn variant.
  Baud rate 300 or 1200.
  Driven by a 6850 ACIA, through the serial ULA.
  Cassette and RS423 ports could not be used at the same time.