Bus mouse

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Template icon--Diagram.svg This article requires illustration in the form of diagrams — 9-pin D-sub diagram is missing

A bus mouse is a mouse (or trackball) which provides readings of its rotary encoder's and buttons switches on dedicated lines to its host at logic levels. Bus mice were often shipped with a computer or with an expansion card; Thus, "bus mouse" is a class of device, not a single standard. This is the simplest class of interface, and all variants are considered obsolete, now being used almost exclusively by retro-computing enthusiasts.

The term as such is most associated with IBM-compatible PCs. Bus mice were contemporary with and competed with serial mice. Once Microsoft had made its implementation: InPort, the term was increasingly used for that specifically. Use of bus mice on PC's fell with the adoption of IBM's PS/2 mouse port.


Buttons are often simply shorted to ground when pressed, with pull-up resistors on the host side. Button input often needs to be debounced, which because buttons are few and wired direct (there is no button matrix) is typically done through a low-pass filter for each input on the host side.

An opto-mechanical mouse sensor contains a mouse ball and an optomechanical rotary encoder on each axis (X and Y). Each encoder produces a "quadrature code" (also called 2-bit Gray code, or "pulse trains") on a pair of lines, which is filtered to logic levels, often by a pair of schmitt triggers in the mouse. In the pinouts below, the lines have been named (XA,XB) and (YA,YB) so that when moving (moving right/down) the sequence for a pair of inputs is: (0,0), (1,0), (1,1), (0,1). The quadrature code sequence for decreasing value (moving left/up) is in the opposite order.

In several implementations (Archimedes, Atari ST, NeXT non-ADB), the mouse is connected to the keyboard and quadrature code is interpreted by the keyboard's microcontroller, which in turn presents mouse input intermixed with keyboard input to the host over a type of serial protocol. On some machines, the ports were also used for game controllers (Apple IIc, Atari ST, Commodore Amiga).

8 pin mini-DIN

View of 8-pin mini-DIN socket
NeXT pin[1] Assignment
1 +5V
2 XA
3 XB
4 YA
5 YB
6 Right button
7 Left button
8 Signal ground
Shell Chassis ground

NeXT (non-ADB)

The mouse shipped with the "NeXT Cube" was a bus mouse which plugged into the keyboard. The keyboard was plugged into the monitor screen, and used a proprietary serial protocol. The monitor in turn was plugged into the computer.

9-pin mini-DIN

View of 9-pin mini-DIN socket
Microsoft Archimedes Assignment
1 6 +5V
2 5 XA
3 1 XB
4 9 YA
5 7 YB
6 2 Left button
7 3 Middle button
8 8 Right button
9 4 Signal ground
Shell Shell Chassis ground

Acorn Archimedes

Mice shipped with the Acorn Archimedes home/office computers. [2] [3]

Microsoft InPort

Microsoft mice could come bundled with an InPortTM ISA card to be installed in the PC. Rumour has it that the chip on Microsoft's InPort card could be reconfigured for other types of peripherals, but no product other than mouse is known.

Many third-party peripherals were sold with just a Microsoft-compatible "Bus mouse" connector.

NEC PC-98xx series computers use Microsoft's pinout[4]

9-pin D-sub, female plug

Atari Amstrad Commodore Assignment
2 1 2 XA
1 2 4 XB
3 4 1 YA
4 3 3 YB
5 n/a 5 Middle button
6 6 6 Left button
7 7 7 +5V
8 8 8 Signal ground
9 9 9 Right button
n/a n/a Shell Chassis ground

Female DE-9 plug, male socket. Must not be confused with a 9-pin serial port. Serial mice' plugs tend to have thumbscrews, but on the Amiga, Atari and Amstrad, the cable's plugs did not, and some ports did not fit those plugs either.

Some third-party mice were made both for the Commodore Amiga and Atari ST, with a switch to select which system it was used with. The Commodore Amiga and Atari ST mouse ports were also used for game controllers, and have thus inherited much of the Atari joystick pinout.

Amstrad PCs however, have separate mouse and joystick ports that are not compatible with one-another.

Atari ST

The Atari ST has two DE-9 controller ports, the first for a mouse (or joystick) and the second only for a joystick). Both were interpreted by the keyboard's microcontroller. The left mouse button is the same as the first joystick Fire button, and the right mouse button is wired to the second port's joystick-Fire button input.

Atari PC

Atari PC's have a Atari ST-compatible mouse port on the motherboard.[5]. The Atari PC supported also a third mouse button, but were shipped with the same two-button mouse as the Atari ST, only relabelled from "STM1" to "PCM1". [6].

Amstrad PC

The Amstrad bus mouse port was on the motherboards of Amstrad PC-1512[7] ,PC-1640[8] and Sinclair PC-200[9] (made by Amstrad).

A curious detail is that the two mouse buttons' lines were fed over the keyboard cable to the keyboard and reported by it as key codes.

Commodore Amiga

Commodore Amiga with AmigaOS were shipped with a two-button mouse. Commodore made a three-button mouse only for the Amiga 3000UX that ran Amiga UNIX but many third-party Amiga mice also came with middle-button. On the Amiga, quadrature signals are interpreted by circuitry in its custom chipset, with mouse support for both of its control ports. A second Amiga mouse is used only in some two-player games, but the second port's circuitry could also be used for rotary controllers such as steering wheels.

In the late 1990s, there appeared third-party Amiga mice with scroll wheels and up to five buttons. A special driver and utility are required to use them. Pin 5, which is analogue-capable (originally for paddle controllers) is used to send this input as varying current. The third mouse-button is represented differently than earlier.[10]

Commodore PC

The Commodore PC-1, PC-10-III, PC-20-III, PC-30 and Colt have a single Amiga-compatible bus mouse port on the motherboard.[11][12]

9-pin D-sub, male plug

Male DE-9 plug, female socket.

Apple pin PC-98 pin Assignment
1 n/a Chassis ground
2 1 +5 VDC
3 9 Signal ground
4 2 XA
5 3 XB
n/a 8 Right Button
7 6 Left/Button
8 5 YB
9 4 YA


Apple shipped bus mice with the Apple Lisa, the original Macintosh 128, Macintosh 512 and Macintosh Plus.

There was also an expansion "Mouse Card" for the Apple II line. The Apple IIc has mouse hardware support built in, where the same port is also used to connect game controllers (whereas on other Apple II computers, mouse and game port would be separate). [13]


Two mouse buttons are supported. [14] The pin numbering is the same as for 9-pin mini-DIN.


Bus mouse to serial port

Bus mouse to USB

  • Retronic Design sells a microcontroller adaptor for devices with female and male DE-9 plug, with free schema and firmwares (.hex files and source code) for many different devices, including Apple, Amiga and Atari mice, plus game controllers.
  • 2600-daptor. Supports a large number of devices with female DE-9 port, including Amiga and Atari ST mice. Uses DIP switches or auto-detect if holding down first button when connecting.

PS/2 to vintage computer

  • Electronica4u]'s Jerry and Jerry+ adaptors for using a PS/2 mouse with USB connector with an Amiga or Atari ST. Jerry+ has a passthrough for a joystick. Usually sold on eBay.

USB to vintage computer

External links


  1. Asterontech—Logitech TrackMan T-PA1-9MD Bus Mouse to NeXT non-ADB. Retrieved 2019-04-11
  2. Documentation for SmallyMouse2 – Universal USB to Quadrature Mouse Adapter
  3. Chris's Acorn—Acorn Archimedes 500 series, Acorn R200 series Service Manual. Retrieved 2019-04-12
  4. http://nkmm.org/yagura/lib/
  5. Atari PC Owner's manual Scan on ataripc.net. Page 65. Dated 1987. Retrieved 2019-03-24
  6. AtariPC.net—PC3 8088. Retrieved 2019-03-24
  7. Amstrad PC1512 Technical Reference Manual. Copy on John Elliott's homepage, retrieved 2019-03-29
  8. AMSTRAD PC1640 TECHNICAL MANUAL. Copy on John Elliott'shomepage, retrieved 2019-03-29
  9. The Vintage Computer Club Malta—SINCLAIR PC 200. Retrieved 2019-03-26
  10. Micromys.de—Micromys support page - Amiga mouse mode with wheel support. Dated 2000. Retrieved 2019-03-24
  11. Ancient Electronics blog—Commodore Colt (Commodore PC10-III, PC20-III)
  12. The 8-bit Guy on Youtube—Commodore History Part 6 - The PC Compatibles. Posted 2019-06-02
  13. Pinouts.ru—Macintosh Mouse pinout. Dated 2017-05-30. Retrieved 2019-04-11
  14. USBマウス・USBキーボードをPC-9801に接続する変換器の製作 ("Production of converter to connect USB mouse and USB keyboard to PC-9801"). Dated 2017-09-10. Retrieved 2019-04-12