mouse - serial mouse interface
Serial mice are connected to a serial RS232/V24 dialout line, see
ttyS(4)
for a description.
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 for synchronization purposes.
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 |
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 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.
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.
The
Sun protocol is the 3-byte version of the above 5-byte Mousesystems
protocol: the last two bytes are not sent.
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 |
- /dev/mouse
- A commonly used symbolic link pointing to a mouse
device.
ttyS(4),
gpm(8)