MOUSE(4)                                            Linux Programmer's Manual                                           MOUSE(4)



NAME
       mouse - serial mouse interface

CONFIGURATION
       Serial mice are connected to a serial RS232/V24 dialout line, see ttyS(4) for a description.

DESCRIPTION
   Introduction
       The pinout of the usual 9 pin plug as used for serial mice is:

                                                   pin   name   used for
                                                     2    RX    Data
                                                     3    TX    -12 V, Imax = 10 mA
                                                     4   DTR    +12 V, Imax = 10 mA
                                                     7   RTS    +12 V, Imax = 10 mA
                                                     5   GND    Ground

       This is the specification, in fact 9 V suffices with most mice.

       The  mouse  driver  can  recognize a mouse by dropping RTS to low and raising it again.  About 14 ms later the mouse will
       send 0x4D ('M') on the data line.  After a further 63 ms, a Microsoft-compatible 3-button mouse will send 0x33 ('3').

       The relative mouse movement is sent as dx (positive means right) and dy (positive means down).  Various mice can  operate
       at  different  speeds.  To select speeds, cycle through the speeds 9600, 4800, 2400 and 1200 bit/s, each time writing the
       two characters from the table below and waiting 0.1 seconds.  The following table shows available speeds and the  strings
       that select them:

                                                            bit/s   string
                                                            9600    *q
                                                            4800    *p
                                                            2400    *o
                                                            1200    *n

       The first byte of a data packet can be used to synchronization purposes.

   Microsoft protocol
       The  Microsoft protocol uses 1 start bit, 7 data bits, no parity and one stop bit at the speed of 1200 bits/sec.  Data is
       sent to RxD in 3-byte packets.  The dx and dy movements are sent as two's-complement, lb  (rb)  are  set  when  the  left
       (right) button is pressed:

                                             byte   d6   d5    d4    d3    d2    d1    d0
                                                1   1    lb    rb    dy7   dy6   dx7   dx6
                                                2   0    dx5   dx4   dx3   dx2   dx1   dx0
                                                3   0    dy5   dy4   dy3   dy2   dy1   dy0

   3-button Microsoft protocol
       Original  Microsoft  mice  only have two buttons.  However, there are some three button mice which also use the Microsoft
       protocol.  Pressing or releasing the middle button is reported by sending a packet with  zero  movement  and  no  buttons
       pressed.  (Thus, unlike for the other two buttons, the status of the middle button is not reported in each packet.)

   Logitech protocol
       Logitech  serial  3-button  mice  use  a different extension of the Microsoft protocol: when the middle button is up, the
       above 3-byte packet is sent.  When the middle button is down a 4-byte packet is sent, where the 4th byte has  value  0x20
       (or  at least has the 0x20 bit set).  In particular, a press of the middle button is reported as 0,0,0,0x20 when no other
       buttons are down.

   Mousesystems protocol
       The Mousesystems protocol uses 1 start bit, 8 data bits, no parity and two stop bits at the speed of 1200 bits/sec.  Data
       is sent to RxD in 5-byte packets.  dx is sent as the sum of the two two's-complement values, dy is send as negated sum of
       the two two's-complement values.  lb (mb, rb) are cleared when the left (middle, right) button is pressed:


                                      byte   d7    d6     d5     d4     d3     d2     d1     d0
                                         1   1     0      0      0      0      lb     mb     rb
                                         2   0    dxa6   dxa5   dxa4   dxa3   dxa2   dxa1   dxa0
                                         3   0    dya6   dya5   dya4   dya3   dya2   dya1   dya0
                                         4   0    dxb6   dxb5   dxb4   dxb3   dxb2   dxb1   dxb0
                                         5   0    dyb6   dyb5   dyb4   dyb3   dyb2   dyb1   dyb0

       Bytes 4 and 5 describe the change that occurred since bytes 2 and 3 were transmitted.

   Sun protocol
       The Sun protocol is the 3-byte version of the above 5-byte Mousesystems protocol: the last two bytes are not sent.

   MM protocol
       The MM protocol uses 1 start bit, 8 data bits, odd parity and one stop bit at the speed of 1200 bits/sec.  Data  is  sent
       to RxD in 3-byte packets.  dx and dy are sent as single signed values, the sign bit indicating a negative value.  lb (mb,
       rb) are set when the left (middle, right) button is pressed:

                                          byte   d7   d6    d5    d4    d3    d2    d1    d0
                                             1   1     0     0    dxs   dys   lb    mb    rb
                                             2   0    dx6   dx5   dx4   dx3   dx2   dx1   dx0
                                             3   0    dy6   dy5   dy4   dy3   dy2   dy1   dy0

FILES
       /dev/mouse
              A commonly used symlink pointing to a mouse device.

SEE ALSO
       ttyS(4), gpm(8)

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      1996-02-10                                                   MOUSE(4)