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 (aqMaq) on the data line.
After a further 63 ms, a Microsoft-compatible 3-button mouse will send
0x33 (aq3aq).
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.
This page is part of release 3.14 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/.
