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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

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