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MOUSE

Section: Linux Programmer's Manual (4)
Updated: 1996-02-10
Index Return to Main Contents
 

NAME

mouse - serial mouse interface  

CONFIG

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:
pinnameused for
2RXData
3TX-12 V, Imax = 10 mA
4DTR+12 V, Imax = 10 mA
7RTS+12 V, Imax = 10 mA
5GNDGround

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/sstring
9600*q
4800*p
2400*o
1200*n

The first byte of a data packet can be used to synchronisation 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:
byted6d5d4d3d2d1d0
11lbrbdy7dy6dx7dx6
20dx5dx4dx3dx2dx1dx0
30dy5dy4dy3dy2dy1dy0
 

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:
byted7d6d5d4d3d2d1d0
110000lbmbrb
20dxa6dxa5dxa4dxa3dxa2dxa1dxa0
30dya6dya5dya4dya3dya2dya1dya0
40dxb6dxb5dxb4dxb3dxb2dxb1dxb0
50dyb6dyb5dyb4dyb3dyb2dyb1dyb0

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:
byted7d6d5d4d3d2d1d0
1100dxsdyslbmbrb
20dx6dx5dx4dx3dx2dx1dx0
30dy6dy5dy4dy3dy2dy1dy0
 

FILES

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

SEE ALSO

ttyS(4), gpm(8)


 

Index

NAME
CONFIG
DESCRIPTION
Introduction
Microsoft protocol
3-button Microsoft protocol
Logitech protocol
Mousesystems protocol
Sun protocol
MM protocol
FILES
SEE ALSO




Random Man Pages:
EVP_CIPHER_CTX_ctrl
atc
mouse
halo