Howto Setup 3 Button Serial Mouse in Linux

Posted on 4:14 PM by Bharathvn

How to get a 3 button serial mouse working properly under Linux.

Table of Contents

1. Disclaimer

2. Introduction

3. Serial Ports

4. Switched Mice

5. Normal Mice

6. Switching a Mouse to 3-Button Mode

7. Wheeled mice

8. Using gpm to Switch Mouse Modes

9. Using two mice

10. XF86Config and Xconfig file examples

11. Cables, extensions and adaptors

12. Miscellaneous Problems and Setups

13. Models Tested

14. Further Information

15. Mouse Tail


1. Disclaimer

The following document is offered in good faith as comprising only
safe programming and procedures. No responsibility is accepted by the
author for any loss or damage caused in any way to any person or
equipment, as a direct or indirect consequence of following these

2. Introduction

The most recent version of this document can always be found at

There is a Japanese translation at
ftp/euc/3-Button-Mouse.euc; and a French one at Other
translations may be available - check your local LDP mirrors.

Most X applications are written with the assumption that the user will
be working with a 3 button mouse. Serial mice are commonly used on
computers and are cheap to buy. Many of these mice have 3 buttons and
claim to use the Microsoft protocol, which in theory means they are
ideal for the X windows setup. (The record for the cheapest working 3
button mouse currently stands at $1.14!)

Most dual-protocol mice will work in two modes:

· 2-button Microsoft mode.

· 3-button MouseSystems mode.

This document leads you through the different steps needed to
configure your mouse in these two different modes, especially the
steps needed to use the more useful 3-button mode.

As distributions become easier to set up, some of the problems ought
to go away. For instance, RedHat have a mouseconfig program to set
things up for you. However, some versions of RH5.0 had a bug in
mouseconfig, so make sure you check for patches.

3. Serial Ports

The first thing to do is to make sure the software can find the mouse.
Work out which serial port your mouse is connected to - usually this
will be /dev/ttyS0 (COM1 under DOS) or /dev/ttyS1 (COM2). (ttyS0 is
usually the 9 pin socket, ttyS1 the 25 pin socket, but of course there
is no hard and fast rule about these things.) There are also an
equivalent number of /dev/cua devices, which are almost the same as
the ttyS ones, but their use is now discouraged. For convenience make
a new link /dev/mouse pointing at this port. For instance, for ttyS0:

ln -s /dev/ttyS0 /dev/mouse

4. Switched Mice

Some mice, not usually the cheapest ones, have a switch on the bottom
marked `2/3'. Sometimes this may be `PC/MS'. In this case the `2'
setting is for 2 button Microsoft mode, and the `3' for 3 button
MouseSystems mode. The `PC/MS' switch is a bit more complicated. You
will probably find the `MS' setting is for Microsoft, and the `PC' is
for MouseSystems. You may find the `PC' setting described as ps/2
mode, but it should do MouseSystems as well. If you have such a
mouse, you can switch the switch to `3' or `PC', put the MouseSystems
settings in your XConfigs (see below) and the mouse should work
perfectly in 3-button mode.

5. Normal Mice

If you don't have any switches, and no instructions, then a little bit
of experimentation is needed. The first thing to try is to assume the
mouse maker is telling the truth, and the mouse is full Microsoft. Set
up your Xconfigs to expect a Microsoft mouse (see the Xconfig section)
and give it a try.

If the mouse didn't work at all, then you don't have a Microsoft
mouse, or there is some other problem. Try the other protocols in the
configs, the man page for the config file is the best place to start
looking. Also look in the Miscellaneous Problems section below.

What you will probably find is that when you run X, the mouse works
fine but only the outer two buttons do anything. You can of course
accept this, and emulate the third button (press both buttons at once
to click the middle one) like you do with a two button mouse. To do
this, change your Xconfig file as shown in the Xconfig example section
below. This may mean you have bought a 3 button mouse for no good
reason, and you are certainly no further forward. So, now you need to
look at your hardware.

6. Switching a Mouse to 3-Button Mode

Even cheap mice can also work under the Mouse Systems protocol, with
all three buttons working. The trick is to get the mouse to think
it's a Mouse Systems one, something you rarely see in your

· Before you power up your computer, hold down the left mouse button
(and keep it held down until it has booted to be on the safe side).

When the mouse first gets power, if the left button is held down it
switches into Mouse Systems mode. A simple fact, but not always
publicised. Note that a soft reboot of your computer may not cut the
mouse power and therefore may not work. There are a number of other
ways of switching the mode, which may or may not work with your
particular mouse. Some of these are less drastic than rebooting your
computer, two are more so!

· If your computer is get-at-able you can unplug the mouse and plug
it back in with the button held down (although you shouldn't
normally plug things in to a live computer, the RS232 spec says it
is OK).

· You may be able to reset the mouse by typing echo "*n" >
/dev/mouse, which should have the same effect as unplugging it.
Hold the left button down for Mouse Systems mode, not for
Microsoft. You could put this in whatever script you use to start X

· Bob Nichols ( has written a small c
program to do the same thing, which may work if echo "*n" does not
(and vice versa). You can find a copy of his source code at

· Someone has reported that the `ClearDTR' line in the Xconfig is
enough to switch their mouse into Mouse Systems mode.

· If you are brave enough, open the mouse up (remember that this will
invalidate your warranty) and have a look inside. In some cases,
the mouse may have a switch inside, for some strange reason known
only to the manufacturer. More likely on the cheap mice is a jumper
which you can move. The switch or jumper may have the same effect
as a `MS/PC' switch described in the ``Switched Mice section''
above. You may find that the circuit board is designed for a
switch between 2 & 3 buttons, but it hasn't been fitted. It will
look something like:

| o | o | o | SW1
1 2 3

Try linking pins 1-2 or 2-3, and see if it changes the behaviour of
the mouse. If it does, you can either fit a small switch, or solder
across the contacts for a quick and permanent solution.

· Another soldering solution which might be a last-resort for mice
which don't understand MouseSystems at all, from Peter Benie
( If the middle button's switch is
double-pole, connect one side of the switch to the left button's
switch, and the other side to right button's switch. If it's not a
double pole switch then use diodes rather than wire. Now, the
middle button pushes the left and right buttons down together.
Select ChordMiddle in the XF86Config and you have a working middle

· The ultimate recourse with the soldering iron was first described
to me by Brian Craft ( Two common
generic mouse chips are the 16 pin Z8350, and the 18 pin HM8350A.
On each of these chips, one pin controls the mode of the chip, as

Pin 3 Mode
----- ----
Open Default Microsoft. Mouse Systems if a button is held on power-up.
GND Always Mouse Systems.
Vdd Always Microsoft.

(Pins are numbered as follows:)

pin1 -| \/ |-
pin2 -| |-
pin3 -| |-
-| |-
-| |-
-| |-
-| |-
pin8 -|____|-

(This info comes courtesy of Hans-Christoph Wirth, and Juergen Exner,
who posted it to de.comp.os.linux.hardware) You can solder a link
between pin 3 and gnd, which will fix the mouse into MouseSystems

· Peter Fredriksson ( has tried the SYSGRATION
SYS2005 chip, and found that linking Pin 3 to Gnd forced Mouse
System mode.

· Uli Drescher ( confirms it works on an HN8348A
chip; Ben Ketcham ( confirms the
HM8348A (Pin 9 is Gnd).

· Urban Widmark ( says the same applies to the
EC3567A1 chip, where Pin 8 is ground. I've tried it as well and it
works fine.

· Timo T Metsala ( has found that on the
HT6510A chip pin 3 is mode select, pin 9 is Gnd. The same works
for the HT6513A chip. Holtek also make HT6513B and HT6513F chips -
on these, pin 8 is Gnd.

· Robert Romanowski ( says pin 3 - pin 8 (Gnd)
works on an EM83701BP chip too.

· Robert Kaiser ( confirms that pin 3 - Gnd works on
a EC3576A1 chip too.

· Sean Cross ( found it was pin 2 - pin 7 (Gnd)
on a HM8370GP chip.

· Peter Fox ( used pin 3 - pin 8 on a
HM8348A chip.

· Jon Klein ( found pin 3 - pin 9 did the
trick for a UA5212S chip.

· As an alternative to the above soldering methods, you can get the
mouse to hold it's own button down when booting: this circuit from
Mathias Katzer.

--- R ---------O------ + Supply
| ----- | | C = 100nF capacitor
| | E | R = 100kOhm
| __ / | T = BC557 transistor
| / \ O
| B | #V | T /
|-----|-# | / Left button switch of the mouse
| | #\ | O
| \__/ |
--- \ C |
--- C ------O----------> (to somewhere deep inside the mouse)
### Ground

The test mouse was a no-name model MUS2S - whether this works in other
mice depends on the circuit of the mouse; if the switch is connected
to ground and not to +Supply, an npn-transistor like the BC547 should
work; R and C have to be swapped then, too.

So there you have it, the choice is yours. Stick with the default
Microsoft two buttons, or work out how to switch the mode and set X up
to take advantage of this.

7. Wheeled mice

Mice with wheels have emerged in the last few years, starting with the
Microsoft Intellimouse and spreading to other manufacturers. The
wheel can be clicked like a button, or rolled up and down. Far and
away the best reference for information is which describes
how to get lots of X applications to recognise the scrolling action.

In general, you'll need a fairly new Xserver to use the scrolling
action, but some older servers will recognise the clicking actions.
For instance, the Intellimouse is supported by XFree 3.3.1 and later.

8. Using gpm to Switch Mouse Modes

gpm is the program that lets you use the mouse in console mode. It is
usually included in linux distributions, and can be started from the
command line or in the startup script /etc/rc.d/rc.local. Note that
distributions don't always have the most recent version (1.13 at time
of writing) which can be found on mirrors of

The main modes for serial mice under gpm are:

gpm -t ms
gpm -t msc
gpm -t help

for Microsoft or MouseSystems modes, or to probe the mouse for you and
tell you what it found. To run gpm in MouseSystems mode, you may need
a -3 flag, and possibly a DTR option, using the -o dtr flag:

gpm -3 -o dtr -t msc

gpm is often able to recognise all three buttons of the mouse even in
Microsoft mode. And newer versions (Version 1.0 and later (?)) can
then make this information available to other programs. For this to
work, you need to run gpm with the -R tag, like this:

gpm -R -t ms

This will make gpm re-export the mouse data to a new device, called
/dev/gpmdata, which looks like a mouse to any other program. Note
that this device always uses the MouseSystems protocol. You can then
set your Xconfig to use this instead of /dev/mouse as shown below, but
of course you must ensure gpm is always running when you use X. Some
people have reported that some middle-button events are not correctly
interpreted by X using this technique, this may be down to an individ­
ual mouse setup.

Changing button mapping for gpm and X (

You may find that gpm uses different default button mappings to X, so
using both systems on the same machine can be confusing. To make X
use the same buttons for select and paste operations as gpm, use the X

xmodmap -e "pointer = 1 3 2"

which causes the left button to select and the right button to paste,
for either 2-button or 3-button mice. To force gpm to use the X stan­
dard button mapping, start it with a -B command, eg:

gpm -t msc -B 132

9. Using two mice

In some cases, for instance a laptop with a built-in pointing device,
you may wish to use a serial mouse as a second device. In most cases
the built-in device uses the PS/2 protocol, and can be ignored if you
don't wish to use it. Simply configure gpm or X to use /dev/ttyS0 (or
whatever) as usual.

To use both at once, you can use gpm -M to re-export the devices.
More details in the gpm man page. Also, XFree 3.3.1 and later support
muliple input devices, using the XInput mechanism. Auto-generated
XF86Config files should have the necessary comments in them.

10. XF86Config and Xconfig file examples

The location of your configuration file for X depends on the
particular release and distribution you have. It will probably be
either /etc/Xconfig, /etc/XF86Config or /usr/X11/lib/X11/XF86Config.
You should see which one it is when you start X - it will be echoed to
the screen before all the options are displayed. The syntax is
slightly different between the XF86Config and Xconfig files, so both
are given.

Microsoft Serial Mouse

· XF86config:

Section "Pointer"
Protocol "microsoft"
Device "/dev/mouse"

· Xconfig:

# Mouse definition and related parameters
Microsoft "/dev/mouse"

Microsoft Serial Mouse with Three Button Emulation

· XF86config:

Section "Pointer"
Protocol "microsoft"
Device "/dev/mouse"

· Xconfig:

# Mouse definition and related parameters
Microsoft "/dev/mouse"

MouseSystems Three Button Serial Mouse

· XF86config:

Section "Pointer"
Protocol "mousesystems"
Device "/dev/mouse"
ClearDTR # These two lines probably won't be needed,
ClearRTS # try without first and then just the DTR

· Xconfig:

# Mouse definition and related parameters
MouseSystems "/dev/mouse"
ClearDTR # These two lines probably won't be needed,
ClearRTS # try without first and then just the DTR

Microsoft Serial Mouse with gpm -R

· XF86config:

Section "Pointer"
Protocol "MouseSystems"
Device "/dev/gpmdata"

· Xconfig:

# Mouse definition and related parameters
MouseSystems "/dev/gpmdata"

11. Cables, extensions and adaptors

The only wires needed in a mouse cable are as follows: TxD and RxD for
data transfer, RTS and/or DTR for power sources, and ground.
Translated into pin numbers, they are:

9-pin port 25-pin port
TxD 3 2
RxD 2 3
RTS 7 4
DTR 4 20
Gnd 5 7

The above table may be of use if you wish to make adaptors between 9-
and 25-pin plugs, or extension cables.

12. Miscellaneous Problems and Setups

· If you have trouble with your mouse in X or console mode, check you
are not running a getty on the serial line, or anything else such
as a modem for that matter. Also check for IRQ conflicts.

· It is possible that you need to hold down the left button when
booting X windows. Some systems may send some sort of signal or
spike to the mouse when X starts.

· Problems with serial devices may be due to the serial port not
being initialised correctly at boot. This is done by the setserial
command, run from the start-up script /etc/rc.d/rc.serial. Check
the man page for setserial and the Serial-HOWTO for more details.
It may be worth a little experimentation with types, for instance
try setserial /dev/mouse uart 16550 or 16550a regardless of what
port you actually have. (For instance, mice don't like the

· The ClearDTR flag may not work properly on some systems, unless you
disable the RTS/CTS handshaking with the command:

stty -crtscts < /dev/mouse

(Tested on UART 16450/Pentium by Vladimir Geogjaev geog­

· Logitech mice may require the line ChordMiddle to enable the middle
of the three buttons to work. This line replaces Emulate3Buttons or
goes after the /dev/mouse line in the config file. You may well
need the ClearDTR and ClearRTS lines in your Xconfig. Some
Logitech mice positively do not need the ChordMiddle line - one
symptom of this problem is that menus seem to move with the mouse
instead of scrolling down. (From:

· Swapping buttons: use the xmodmap command to change which physical
button registers as each mouse click. eg: xmodmap -e "pointer = 3
2 1" will turn round the buttons for use in the left hand. If you
only have a two-button mouse then it's just numbers 1 & 2.

· Acceleration: use the xset m command to change the mouse settings.
eg xset m 2 will set the acceleration to 2. Look at the manpage
for full details.

· Pointer offset: If the click action appears to be coming from the
left or right of where the cursor is, it may be that your screen is
not aligned. This is a problem with the S3 driver, which you may be
able to fix using xvidtune. Try Invert_VCLK/InvertVCLK, or EarlySC.
This info from Bill Lavender (lavender@MCS.COM) and Simon Hargrave.
In the XF86Config, it might look like this:

Subsection "Display"
Modes "1024x768" "800x600" "640x480" "1280x1024"
Invert_VCLK "*" 1

· If you are getting `bouncing' of the mouse buttons, ie two clicks
when you only wanted one, there may be something wrong with the
mouse. This problem has been solved for Logitech mice by Bob
Nichols ( and involves soldering some
resistors and a chip in the mouse to debounce the microswitches.

· If some users cannot get the mouse to work but some (eg root) can,
it is possible that the users are not running exactly the same
thing - for instance a different version of X or a different
Xconfig. Check the X start-up messages carefully to make sure.

· If you find the mouse pointer is erasing things from your screen,
you have a server config problem. Try adding the option linear, or
maybe nolinear to the graphics card section, or if it is a PCI
board, the options tgui_pci_write_off and tgui_pci_read_off. (This
seems to be a Trident Card problem.)

· If the mouse cursor doesn't show up on the screen, but otherwise
seems to be working, try the option "sw_cursor" in the Device
section of the config file.

· If your mouse stops working when its sunny or when you turn a light
on, it may be that the sensors are being swamped by light getting
through the case. You could try painting the inside of the case
black, or putting some card in the top.

· Microsoft Brand mice are often a cause of problems. The newest
``Microsoft Serial Mouse 2.1A'' has been reported not to work on
many systems, although unplugging it and plugging it in again may
help. gpm version 1.13 and higher should also support 2.1A mice,
using the pnp mouse type. (See the gpm section for how to re-
export this.) The ``Microsoft Intellimouse'' also causes problems,
although it should now be supported by XFree version 3.3 and later.

13. Models Tested

There are a lot of different mice out there, and I cannot honestly say
that you should go out and buy one rather than the other. What I can
do is give a list of what I think these mice do, based on experience
and heresay. Even with this information you should be a little
cautious - we had two identical mice in our office on two computers,
some things worked on one and not t'other! Any additions to this list
would be welcome.

Mouse Systems optical mouse, serial version
Works well (as you might expect from the name!) without ClearDTR or
ClearRTS in the config.
WiN mouse, as sold by Office World for eight quid.
Standard dual-mode Microsoft/MouseSystems.
Agiler Mouse 2900
Standard dual-mode Microsoft/MouseSystems. SYSGRATION SYS2005 chip is
Sicos mouse,
Works ok, needs ClearDTR & Clear RTS in config.
Index sell a mouse for 10 quid,
Doesn't work in 3 button mode, but does have nice instructions :-)
Artec mouse
Usual dual-protocol mouse, needs `ClearDTR' set in config, NOT
DynaPoint 3 button serial mouse.
Usual dual-protocol mouse, needs `ClearDTR' AND `ClearRTS' in Xconfig.
Genius Easymouse 3 button mouse
Works fine with Mouseman protocol without the ChordMiddle parameter
set. From Roderick Johnstone (
Truemouse, made in Taiwan
Works OK, needs `ClearDTR' in config. (From Tim MacEachern)
Champ brand mouse
Needs to have switch in PC mode, which enables MouseSystems protocol
also. (From
MicroSpeed mouse
Usual dual-protocol mouse.
Venus brand ($7)
Has a jumper inside to switch between 2 and 3 button mode. (From )
Switched mouse, works OK as MouseSystems in 3-button position. (From .)
Manhattan mouse.
Switch for `MS AM' / `PC AT' modes, MS mode works fine with the gpm -R
method. (From
Inland mouse.
Switch for `PC/MS' modes, works fine. (From
qMouse (3-button), FCC ID E6qmouse X31.
Sells in the USA for about $10. Works with `gpm -t msc -r 20'. No
jumpers or switches for MouseSystems 3-button mode. Unreliable in X.
Does not respond to echo "*n" > /dev/mouse.
Mitsumi Mouse (2-button), FCC ID EW4ECM-S3101.
Sells in the USA for about $12. Reliable in X and under gpm, smooth
double-button. (These two from
PC Accessories mouse that i got from CompUSA for under $10.
Has PC/MS switch on bottom. Works OK. (From
First Mouse - seriously cheap at 7.79 pounds at Tempo.
Dual Microsoft/MouseSystems, mode set by button depress at power-up.
No switches, no links. Four wire connection, echo '*n' doesn't work.
`gpm -R' works a treat. (From
Trust 3-button mouse.
Dual-mode with switch, works OK as MouseSystems in `PC' mode. gpm
doesn't like the Microsoft mode.
Chic 410
Works perfectly when kept in ms mode and used with the gpm -R command.
From Stephen M. Weiss (
KeyMouse 3-button mouse.
Works OK with ClearDTR and ClearRTS in Xconfig; `-o dtr' needed with
gpm. (From
Qtronix keyboard `Scorpio 60'
All three buttons work in MouseSystems protocol. (From
Tecra 720 laptop
The glidepoint is on /dev/cua0; the stick is on /dev/psaux. (From
Anubis mouse
Works fine, need to hold down left button whenever switching to the X
virtual console. (From Joel Crisp)
Yakumo No.1900 mouse
Works with gpm -R -t ms exporting to X. (From Oliver Schwank)
Genius `Easy Trak' Trackball
Is not Microsoft compatible, use Mouseman in the Xconfig and it will
work fine. (From
Highscreen Mouse Pro
`Works fine' says
Logitech CA series
Works in X using MMseries protocol, at 2400 Baud, 150 SampleRate.
(Should also apply to Logitech CC, CE, C7 & C9 mice). (From
A4-Tech mouse
Works OK, needs DTR line under both X and gpm. (From
Vertech mouse
Normal Microsoft/Mousesystems behaviour, can be soldered for a
permenant fix. (From
Boeder M-7 ``Bit Star'' (and other M series apart from M13)
Switches to Mousesystems protocol by holding any button down at power-
on. (From
Mouse Systems ``Scroll'' Mouse (four buttons and a roller/button)
Has a 2/3 switch - in mode 3 functions as a three button MouseSystems
mouse, ignoring extra button & wheel. Doesn't need ClearRTS/DTR.
Radio Shack 3-button Serial Mouse
Model 26-8432, available in Tandy for about 20 quid. Works as
Mousesystems with ClearDTR. (From
Dexxa serial mouse
Works fine using Microsoft protocol in Xconfig, no ChordMiddle or
anything needed. (From
Belkin 3 button mouse
As purchased from Sears (\$10), needs -o rts under gpm (and probably
ClearRTS under X) when in PC mode. (From

14. Further Information

· Mouse Systems has a web site at They
have a Windows driver if you need one.

· The Linux Serial HOWTO is available from mirrors of sunsite around
the world. If you don't know where your nearest mirror is, start

· There is a very good explanation of how mice work at

· Fuller details of the Xconfig and XF86Config files are found on the
relevant man pages, and in the documentation about installing X
windows such as the Xfree86 HOWTO. Also, see the XFree86 FAQ at a
mirror of

· Information about gpm can be found on the man page, also try the
web page of Darin Ernst at

· Lots of information on mice hardware and software can be found at

15. Mouse Tail

Much of the information for this document has been trawled from the
various linux newsgroups. I am sorry I did not keep a record of
everyone who has indirectly contributed by this route, thank you all
very much.

So, to sum up:

· Even cheap 3 button Microsoft mice can be made to work.

· Configure your copy of X to expect a Mouse Systems mouse.

· Hold down the left button at power-on to switch the mouse to
MouseSystems mode.

· You might need to hold the left button down when starting X.

· Mice are more intelligent than you think.