Mouse Connector
Mouse Connector Pinouts
Mouse Connector Signals
Serial, Bus, and PS/2 Mice
Using Serial Mice on a PS/2?
IBM Mouse Types
PS/2 to Serial to PS/2 IBM PS/2 Mouse Program Diskette Ver 1.00 
PS/2 Mouse Maker

Location of Mouse (pointing device) connector.
  The PS/2 mouse port is IRQ 12 and I/O Port Addresses 60h and 64h.

Bus Mouse Problem!
   A bus mouse uses a mini-DIN connector just like the PS/2 mouse, although they are totally incompatible. You can damage your motherboard by plugging a bus mouse into it. 
NOTE:  Microsoft calls it's bus mouse an Inport mouse Be warned!

Mouse Connector Pinout
   The keyboard connector is a 6-pin miniature DIN connectors. The signals and voltages are the same for both connectors.

+ 5 V dc

The keyboard and auxiliary device signals are driven by open-collector drivers pulled to 5Vdc through a pull-up resistor.
Sink current Max
Hi-level output V Min
5.0 Vdc minus pull-up 
Low-level Output v Max
0.5 Vdc 
High-level input v Min
2.0 Vdc 
Low-level input v Max
0.8 Vdc 

Serial Mouse Conversion?
   The "Serial Mouse" uses a RS-232 style interface with -5 to -12 VDC as logical "1" and +5 to +12 VDC as logical "0". The PS/2 mouse interface is a TTL-style interface, which uses 0 - +2 VDC as logical "0" and +3 - +5 VDC as logical "1".
   In addition - and to make things worser - the RS-232 is an asynchronous interface, the PS/2 interface is a synchronous, where the data is sent along with a clock signal. It uses a simplified 4-wires serial interface with +5VDC (for the transceiver), GND, keyboard / mouse clock and keyboard / mouse data. The data and clock line can be used from the keyboard / mouse controller and the attached device as well following a particular handshake, which defines which is the active "sender" and which is the "receiver". So: it is not *that* easy conversing serial mouse to PS/2 and vice versa.
   The "dual mode" mice have an automatic logic detection and sort of adaptive interface electronic, which detects whether the mouse is attached to a serial port or a PS/2 port and set the output drivers accordingly.
   As you can see from the above: it is not enough only *physically* changing the plugs.

PS/2 Mouse Versions
From Fred Mau

   Best as I can tell, IBM had five distinct species of Rattus Armonkus in the PS/2 world: (Not to mention all the clones).
- The original ugly wedge-shaped PS/2 mouse
- Early oval-shaped mouse. White body and white buttons.
- Later oval-shaped mouse. White body and brownish buttons.
- A smaller black mouse to be used with the CL57and N51 and thinkpad 700 and
720 laptops.  Lower voltage than a regular mouse, not interchangeable.
- The current IBM mouse, OEM'ed  by Logitech. A more ergonomic oval.

   Best as I can tell, all the PS/2 mice (except the minnie mouse for early thinkpads) are interchangeable, with one notable exception:  If you have an 8516 Touchscreen monitor, the touchscreen cable plugs into the mouse port and the mouse plugs into the monitor, but it will ONLY work with the original ugly mouse or the early oval mouse with white buttons. It won't
work with the later oval mouse with brown buttons or anything newer.  I have no idea why, but apparently something changed in the mice.  It's something to keep in mind if you ever happen across an 8516.

From Jim Shorney:
   Side note: I seem to have an oval variation you didn't mention: white top, white buttons, brownish bottom, 33G5430/33G5410/FRU33G5420.
   BTW, have you seen the IBM memo on mouse ball replacement?  Hilarious.

Ed. I think he means THIS

From Carroll Bloyd
   And there's the track-ball/mouse combination (P/N 1397040) sold for use with the L40 SX laptop.  Big ugly thing--the mouse side of the device looks like a larger version of the original PS/2 mouse.
   And, you might want to add the three-button mouse OEM'ed from Logitech and supplied with the 9595-PQx models.  They seem to be rare--I've only seen a few--I wonder if they were used on the RS6000 also?

From David Doerr
   There was, indeed, a three-button mouse from Logitech used on the RS6000.  I have several, but they don't seem to work on my 9590...

Resolution Increase
From Aron Eisenpress
   I'd like to point out one substantive change in the IBM PS/2 mice, which happened around the time of the two-tone-topped ones: the resolution increased from 200dpi to 400dpi (and noticeable if you swap mice around as the speed of the cursor will change!)...

PS/2 mouse to serial cable and back to PS/2 port 
From Tim Clarke
Hi Bill,
   I think your problem is in the PS/2->Serial and Serial->PS/2 adapters. You *must* ensure that they *are* as described and *not* 2 x PS/2->Serial or 2 x Serial->PS/2 used back-to-back. Otherwise, the  pinouts will not get 'passed' correctly.
   The thing to be aware of is that, with a manual switch, the keyboard and mouse 'lose' power during a switch and 'reinitialise' when the switch closure to the 'to' computer is completed (i.e. 5V power returns). Also, you can get spurious bytes sent during the transitions.
    As I said, DOS (due to BIOS) and the OS/2 (due t their drivers and haven't implemented the equivalent functionality that would cause you to 'lose' mouse and/or keyboard function (except for manic beeping for keypresses) after a 'switch-away, switch-back sequence). 
   It may be down to the O/S drivers. E.g. All PS/2 BIOS/ABIOS seem to handle an 'unexpected keyboard reconnection' (i.e. 0xFF bytes and BAT-completion message) and reinitialise the 'Scan Code Set' and 'Shift State' indicators. Mouse stuff seems to be much more sensitive and OS/2 is the only server environment that I *know* can (usually) handle this. Netware 3.1x and 4.1x don't. Windows and WfWg don't. I doubt whether W9x does. NT *might* but I don't know. DOS is happy so long as you're at the command prompt with no mouse-driven s/w actively using the mouse.

Current Mouse Maker
   Unicomp lists the IBM Two Button mouse. It has the brown buttons and the white body. I have a few of this specific model. Nice button switches, tracks well. At $7 it's a damn good bargain. Mine has a long cord (nice for use with 80/85/95 systems!)

96F9275  IBM Two Button mouse Regular $15 Sale $7 

Serial, Bus, and PS/2 Mice
Thanks for the formatting advice, Rich!
 PC Magazine  May 28 1991 v10 n10 p413(4)  * Full Text COPYRIGHT Ziff-Davis Publishing Co. 1991.
Title:     Tutor
Author:    Prosise, Jeff.

Would you describe how the three common types of mice work (serial, bus, and PS/2 mouse port), how the mouse driver communicates with the mouse, and how programs in turn talk to the mouse driver?
Jacek Hejnar, St.  Hubert, Quebec

At the software level, bus mice, serial mice, and PS/2 mice are all the same. The mouse driver provides a common interface so that an application program can communicate with a mouse using identical sets of function callsregardless of its type.

At the hardware level, however, these mouse types are fundamentally different.  The serial mouse works just like a communications device: It sends data to the serial port of your choice each time a mouse event takes place.  (A mouse event is when a button is pressed or released or the mouse is moved.) A microprocessor inside the mouse transmits a packet of data any time it detects a change in state.

Typically, the mouse driver programs the serial port to interrupt the CPU when a byte of data is received at the port.  It does this in the same way a communications program such as ProComm would.

If the mouse is stationary and no buttons are being activated, no CPU time is tied up tracking mouse actions.

Many serial mice use the 3-byte packet format standardized by Microsoft to transmit information about mouse position and the state of the buttons to the CPU.  Figure I shows the format of the packet.  Since the Microsoft Serial Mouse transmits data at 1,200 bits per second using I stop bit, 7 data bits, and no parity, bit 7 (the leftmost bit) in each byte isn't used.  Bit 6 is a clock bit that the mouse driver uses to stay in sync with the mouse.  In the first byte in the packet, it's set to 1; in the second and third bytes, it's set to 0.  Bits 4 and 5 indicate the current up/down states of the left and right mouse buttons.  A 0 indicates that the corresponding button is pressed, while a I indicates that it's not.  The remaining bits in the data packet are combined to form two 8-bit numbers indicating the number of mickeys the mouse has moved in the x (horizontal) and y (vertical) directions since the last report.  A mickey is the mouse unit of distance, equal to approximately 0.005 inch.  By recording mickeys, the mouse driver can track the location of the mouse at all times.


Each time a serial mouse is moved, it transmits a packet of data containing information about the mouse position and the state of the buttons to the CPU. This figure illustrates the 3-byte data packet format that is used by the Microsoft Serial Mouse and many other Microsoft-compatible Serial Mice.

Byte 1
 X | 1 | LB | RB | Y7 | Y6 | X7 | X6 |

Byte 2
 X | 0 | X5 | X4 | X3 | X2 | X1 | X0 |

Byte 3
 X | 0 | Y5 | Y4 | Y3 | Y2 | Y1 | Y0 |

Bit     Description
 X      Not used
 1      Always 1
 0      Always 0
 LB     Left button
           0 = pressed
           1 = not pressed

 RB     Right button
           0 = pressed
           1 = not pressed
 X7-X0  8-bit X-movement indicator (number of mickeys moved in the  horizontal direction since the last data transmission.

 Y7-Y0  8-bit Y-movement indicator (number of mickeys moved in the horizontal direction since the last data transmission.

The mouse driver can determine the direction of the movement-up or down, right or left-from the sign of the mickey counts transmitted by the mouse, which are encoded in two's complement form (a common method for representing signed integers on computers).  Using this representation, an 8-bit value can store any number from -128 to  127, inclusive.  Thus, the mouse can move up to 127 units in either direction (about 0.62 inch) in the time it takes a,packet to be transmitted (about 20 milliseconds at 1,200 bps) without missing a beat.  That provides enough latitude for you to move the mouse across the table rather quickly, without losing any information in the process.  Some mice use higher data rates to increase resolution.  Logitech's Series 9 Mouse, for example, operates at 2,400 bps, doubling the range that the mouse may travel between data transmissions.

Not all serial mice use Microsoft's 3-byte packet format.  The three-button Mouse Systems Mouse, for example, transmits data in 5-byte packets. The added bits are used to transmit information about the third button (something that the Microsoft format does not support) and information about the mouse's current and last positions, which, among other things, can be used to determine mouse velocity.

How does the serial mouse get its power? It's not battery operated, nor does it have to be plugged into an electrical outlet.  Instead, it draws power directly from the serial port through the RTS (request to send) line.  The Microsoft Serial Mouse uses five RS-232 lines: TD (transmit data), RD (read data), DTR (data terminal ready), RTS  ready to send), and SG (signal ground).  TD is used to transmit packets of data.  The driver asserts RTS when it is activated, to make sure power is available to the mouse, and asserts DTR as a signal that it's installed and ready to go.  In current Microsoft Serial Mouse implementations, RD is unused.


The bus mouse interfacing scheme takes an entirely different approach to linking a mouse to a PC.  Unlike the serial mouse, the bus mouse does not contain its own microprocessor.  Instead, logic on the bus interface card is responsible for monitoring the mouse and notifying the mouse driver when the mouse is moved or a button is activated.  In the most common implementation, the card is programmed to poll the mouse at regular intervals (typically every 1/30 to 1/60 second) and interrupt the CPU so that the mouse driver can read the current mouse status from registers on the card.  Why these interrupt rates? Because 30 to 60 Hz roughly corresponds to the refresh rates of most displays.  When the mouse pointer is being moved across the screen, there's usually no need to poll the mouse more frequently, because the screen can't be updated fast enough to show what's happening.  difficult to paint a picture of how a " typical " bus mouse operates.  Versions of the Microsoft Bus Mouse sold since 1986, for example, contain a custom chip called an InPort on the bus interface card.  This chip tracks mouse events and-like the microprocessor in the serial mouse-interrupts the CPU only when the mouse is moved or a mouse button is pressed or released.  This way, valuable CPU time isn't wasted reading registers on the interface card when the mouse is idle. And thanks to the InPort chip, the Microsoft Bus Mouse can be programmed for 30-, 50-, 100-, or 200-Hz operation.  It's also possible to have the InPort chip interrupt the CPU at regular intervals regardless of whether there's anything new to report, or to forgo interrupts altogether and allow software to drive the mouse strictly by polling it.  Using this scheme, the mouse driver (or a program driving the mouse directly) can track mouse position more precisely than programmed 30-to-200-Hz interrupt rates allow. Alternatively, it can tap into the vertical sync pulse generated by the video adapter each time a screen refresh is completed and take time out to read the mouse status during the vertical blanking interval.

A bus mouse does not send packets of data the way the serial mouse does. Instead, status is read directly from lines connecting the mouse to the bus interface card.  For example, the Microsoft Bus Mouse uses the nine-pin Hosiden circular connector shown in Figure 2.  Of the nine pins, three-SWI, SW2, and SW3-reflect the state of up to three mouse buttons in real time. XA, XB, YA, and YB carry quadrature signals that communicate the amount and direction of motion in the x and y directions to counter registers inside the InPort chip.  In quadrature encoding, two lines are provided to track motion in a given direction.  A pulse on one of the lines-for example, XA-indicates that the mouse has been moved.  A pulse on XB, which arrives slightly out of phase with the pulse on XA, reveals the direction of the movement.  If XA leads, then movement is positive; if the pulse on XB comes first, movement is in the negative direction.  Values read from the InPort's counter registers are two's complement 8-bit numbers, so they, like the values transmitted by the serial mouse, may range from -128 to  127.

The remaining two pins on the connector serve equally important functions. The bus mouse draws its power from the +5V pin, while the other pin goes to ground.


The Microsoft Bus Mouse uses a nine-pin circular connector to interface with the bus interface card. SW1, SW2 and SW3 are used to sense the state of the mouse buttons. XA, XB, YA and YB carry quadrature signals indicating mouse movement and  direction. The mouse draws power from the +5V pin, while the remaining pin goes to ground.

      SW2| SW3|    | Signal Ground
         |    |    |
   /     X    X    X       \
  |                        |
  |  XB|  YA|  YB| SW1|    |
  |    |    |    |    |    |
  |    X    X    X    X    |
  |                        |
   \        X    X        /
            |    | 
         +5V|  XA| 

X = Denotes each pin.


The PS/2 mouse is similar to the serial mouse in many respects.  This mouse contains its own microprocessor that transmits clocked serial data to the keyboard controller inside the PS/2, just as the PS/2 keyboard does.  The controller decodes the information coming in and the PS/2 BIOS makes it available to the mouse driver.  Through the BIOS programming interface, the mouse sampling rate may be set to frequencies ranging from 10 to 200 Hz. Typically, the mouse driver will register itself with the BIOS, and the BIOS will activate a handler inside the driver each time a mouse-related event occurs.

One peculiarity of the PS/2 mouse is that the packet format it employs does not include a clock bit as the Microsoft packet does.  Furthermore, because the same system board controller is used to decode data coming from the mouse and the keyboard simultaneously, programs that use both the mouse and keyboard on the PS/2 sometimes experience data-overman conditions that cause the mouse driver to lose synchronicity with the mouse.  If there were a clock bit, timing could be reestablished and the overrun condition could be defeated.  Without the clock bit, application programmers have been forced to resort to several ad hoc means of maintaining the integrity of the
information flowing to the mouse driver.  Some of these methods are more effective than others.  If your mouse goes haywire or simply stops working when you run certain application programs on a PS/2 (especially older programs), it's probably for this reason.

It's no accident that you can replace the end adapter on a Microsoft Serial Mouse and plug it into the mouse port of a PS/2.  The PS/2 mouse port has six pins, one of which carries power to the mouse (see figure 2b).  The Microsoft Serial Mouse looks at this line to determine what type of port it's connected to and adjusts the format of the data it sends out accordingly.  If the line is asserted (carrying voltage), then the mouse knows it's attached to a PS/2 port.  If the line is not asserted, the mouse concludes that it must be attached to a serial port. 


Oops. In Peter's own words, "Wherever you got the PS/2 Mouse connector from: it is total bullshit." 

I assumed the author knew enough to get it right. 

See the real PS/2 Mouse Pinout (towards the top of the page)

This is the illustration from the original text. Not the "AC Commercial Power, Low-Battery Warning Signal" .

Pin #
   1 ----- On-AC Comercial Power    4 ----- Not used
   2 ----- Not Used                 5 ----- Low-Battery-Warning signal (Open)
   3 ----- Ground                   6 ----- Not Used

   /  6  ##  5  \    <==The ## denotes the Notch in the connector.
  |  4        3  |
   \  2      1  /

THE MOUSE PROGRAMMING INTERFACE Fortunately,programs don't have to interface with the mouse at the packet level; that's what mouse drivers are for.  The mouse driver is the program you install before running an application that uses the mouse.  The Microsoft mouse driver is called MOUSE.SYS or MOUSE.COM. (The only difference between the two is that MOUSE.SYS is installed with a DEVICE statement in CONFIG.SYS, while MOUSE.COM is installed from the command line or your AUTOEXEC.BAT file.) Microsoft and Nbcrosoft-compatible mouse drivers provide a set of 35 high-level function calls that applications can use to communicate with the mouse. 


Microsoft and Microsoft-compatible mouse drivers provide 35 different function calls (functions 17 & 18 are not assigned) that a program can use to communicate with the mouse.  Collectively, these function calls make up the mouse programming interface.

Code    Description
 0      Mouse Reset and Status
 1      Show Cursor
 2      Hide Cursor
 3      Get Button Status and Mouse Position
 4      Set Mouse Cursor Position
 5      Get Button press Information
 6      Get Button Release Information
 7      Set Minimum and Maximum Horizontal Cursor Position
 8      Set Minimum and Maximum Vertical Cursor Position
 9      Set Graphics Cursor Block
10      Set Text Cursor
11      Read Mouse Motion Counters
12      Set Interrupt Subroutine Call Mask and Address
13      Light Pen Emulation Mode On
14      Light Pen Emulation Mode Off
15      Set Mickey/Pixel Ratio
16      Conditional Off
17      (Not assigned)
18      (Not assigned)
19      Set Double Speed Threshold
20      Swap Interrupt Subroutines
21      Get Mouse Driver State Storage Requirements
22      Save Mouse Driver State 
23      Restore Mouse Driver State 
24      Set Alternate Subroutine Call Mask and Address
25      Get User Alternate Interrupt Address
26      Set Mouse Sensitivity
27      Get Mouse Sensitivity
28      Set Mouse Interrupt Rate
29      Set CRT Page Number
30      Get CRT Page Number
31      Disable Mouse Driver
32      Enable Mouse Driver
33      Software Reset
34      Set Language for Messages
35      Get Language Number
36      Get Driver Version, Mouse Type and IRQ Number

For example, if a program wants to determine whether a mouse button is currently held down, all it has to do is make a call to function number 5, Get Button Press Information.  The driver, which fields the interrupt generated when a mouse button is pressed or released, keeps track of the state of the buttons.  In response to the program's request, the driver returns an integer whose value reflects the current button status.  If the left button is depressed, bit 0 is set to 1; if the right button is depressed, bit 1 is set to 1.  A value of 0 in either bit indicates that the corresponding button is not depressed.

Mouse driver functions are accessed through interrupt 33h.  The following code sequence portrays what a typical call to the mouse driver looks like in assembly language:

  MOV    AX,5
  MOV    BX,l
  INT    33H
  TEST   BX,l

In general, function codes are passed in register AX, and other parameters in BX, CX, and DX.  This particular sequence calls function 5 to retrieve the status of the right mouse button (BX=l for the right button, BX=O for the left).  On return, bit I of the BX register is tested and a branch is made if it's set to 0, indicating the button is not currently depressed.

We don't have the space here to explore each of the function calls in detail. For more information, refer to the Microsoft Mouse Programmer's Reference (1989, Microsoft Press), or to PC Magazine's July 21, 1987, Lab Notes column ("Mouse Software: See How They Run," page 41 1).  However, there is one function that is so useful and so widely used by programmers that a discussion of the mouse programming interface couldn't be considered complete without it: function 12, Set Interrupt Subroutine Call Mask and Address.

Function 12 lets a program instruct the mouse driver to interrupt it asynchronously when the mouse is moved or a button is pressed or released. The program passes the mouse driver two objects: a call mask and a subroutine address.  The call mask acts as an event filter.  If the program isn't interested in mouse movements or button releases, the call mask can be set up so that the driver interrupts the program only when a button press occurs. The subroutine address is a 32-bit pointer to the subroutine that the program will use to process calls from the mouse driver.  By registering itself with the mouse driver this way, a program doesn't have to constantly poll the mouse driver to see what's going on.  When something happens, the program is automatically notified and given a chance to act on the event.

9595 Planar

9595 Main Page

om the mouse driver.  By registering itself with the mouse driver this way, a program doesn't have to constantly poll the mouse driver to see what's going on.  When something happens, the program is automatically notified and given a chance to act on the event.

9595 Planar

9595 Main Page