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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 rais-
     ing  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  for  synchronization  pur-
     poses.

 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 but-
     tons, 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 val-
     ues,  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 pack-
     ets.  dx and dy are sent as single signed values, the sign bit indicat-
     ing  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 symbolic link pointing to a mouse device.