Mouse IO

Mice are often overlooked as motion or position encoders. Mechanical mice can be connected directly to a shaft and relay data to a uC via serial communication without requiring any processing of encoder data. Optical mice can sense motion without mechanical conneciton and can do so at a distance given an optical refit, allowing them to focus past their bottom surface.

Communications Protocols

The old PS2 mice are valuable because they don't require a complex USB stack to work. They send (after being activated) a simple series of data bytes over standard logic level, bidirectional (open collector) wires. Power is 4.5 to 5.5 volts at up to 275mA. Don't hot plug.

note: much of this shamlessly copied from
http://www.computer-engineering.org/ps2protocol/

The pinouts for each connector are shown below:
 

Male (Plug)

Female  (Socket)

5-pin DIN (AT/XT):  1 - Clock 2 - Data 3 - Not Implemented 4 - Ground 5 - Vcc (+5V)

Male (Plug)

Female (Socket)

6-pin Mini-DIN (PS/2): 1 - Data 2 - Not Implemented 3 - Ground 4 - Vcc (+5V) 5 - Clock 6 - Not Implemented

6-pin SDL: A - Not Implemented B - Data C - Ground D - Clock E - Vcc (+5V) F - Not Implemented

Summary: Bus States
Data = high, Clock = high:  Idle state.
Data = high, Clock = low:  Communication Inhibited.
Clock = low for 100mS, Data = low, Clock = high:  Host Request-to-Send

  All data is transmitted one byte at a time and each byte is sent in a frame consisting of 11-12 bits.  These bits are:

• 1 start bit.  This is always 0.
• 8 data bits, least significant bit first.
• 1 parity bit (odd parity).
• 1 stop bit.  This is always 1.
• 1 acknowledge bit (host-to-device communication only)

PS2 -> Host. PS2 generates 10 - 16.7 kHz clock, host reads data on the falling edge.

Host -> PS2, after Host Request-to-Send, PS2 generates Clock signals and clocks in eight data bits and one stop bit.  The host changes the Data line only when the Clock is low, and data is read by the device when Clock rises.  After the stop bit is received, the device will acknowledge the received byte by bringing the Data line low and generating one last clock pulse.  If the host does not release the Data line after the 11th clock pulse, the device will continue to generate clock pulses until the the Data line is released (the device will then generate an error.) The host may abort transmission at time before the 11th clock pulse (acknowledge bit) by holding Clock low for at least 100 microseconds.

The standard PS/2 mouse sends movement/button information to the host using the following 3-byte packet:

The movement values are 9-bit 2's complement integers, where the most significant bit appears as a "sign" bit in byte 1 of the movement data packet. Their value represents the mouse's offset relative to its position when the previous packet was sent, in units determined by the current resolution. The range of values that can be expressed is -255 to +255. If this range is exceeded, the appropriate overflow bit is set.

Command Set

Following is the set of commands accepted by the standard PS/2 mouse. If the mouse is in stream mode, the host should disable data reporting (command 0xF5) before sending any other commands.

• 0xFF (Reset) - The mouse responds to this command with "acknowledge" (0xFA) then enters reset mode.
• 0xFE (Resend) - The host sends this command whenever it receives invalid data from the mouse. The mouse responds by resending the last packet it sent to the host. If the mouse responds to the "Resend" command with another invalid packet, the host may either issue another "Resend" command, issue an "Error" (0xFC) command, cycle the mouse's power supply to reset the mouse, or it may inhibit communication (by bringing the clock line low). This command is not buffered, which means "Resend" will never be sent in response to the "Resend" command.
• 0xF6 (Set Defaults) - The mouse responds with "acknowledge" (0xFA) then loads the following values: Sampling rate = 100, resolution = 4 counts/mm, Scaling = 1:1, data reporting = disabled. The mouse then resets its movement counters and enters stream mode.
• 0xF5 (Disable Data Reporting) - The mouse responds with "acknowledge" (0xFA) then disables data reporting and resets its movement counters. This only affects data reporting in stream mode and does not disable sampling. Disabled stream mode functions the same as remote mode.
• 0xF4 (Enable Data Reporting) - The mouse responds with "acknowledge" (0xFA) then enables data reporting and resets its movement counters. This command may be issued while the mouse is in remote mode, but it will only affect data reporting in stream mode.
• 0xF3 (Set Sample Rate) - The mouse responds with "acknowledge" (0xFA) then reads one more byte from the host. The mouse saves this byte as the new sample rate. After receiving the sample rate, the mouse again responds with "acknowledge" (0xFA) and resets its movement counters. Valid sample rates are 10, 20, 40, 60, 80, 100, and 200 samples/sec.
• 0xF2 (Get Device ID) - The mouse responds with "acknowledge" (0xFA) followed by its device ID (0x00 for the standard PS/2 mouse). The mouse should also reset its movement counters.
• 0xF0 (Set Remote Mode) - The mouse responds with "acknowledge" (0xFA) then resets its movement counters and enters remote mode.
• 0xEE (Set Wrap Mode) - The mouse responds with "acknowledge" (0xFA) then resets its movement counters and enters wrap mode.
• 0xEC (Reset Wrap Mode) - The mouse responds with "acknowledge" (0xFA) then resets its movement counters and enters the mode it was in prior to wrap mode (stream mode or remote mode).
• 0xEB (Read Data) - The mouse responds with "acknowledge" (0xFA) then sends a movement data packet. This is the only way to read data in remote mode. After the data packet has successfully been sent, the mouse resets its movement counters.
• 0xEA (Set Stream Mode) - The mouse responds with "acknowledge" (0xFA) then resets its movement counters and enters stream mode.
• 0xE9 (Status Request) - The mouse responds with "acknowledge" (0xFA) then sends the following 3-byte status packet (then resets its movement counters):

Right, Middle, Left Btn = 1 if button pressed; 0 if button is not pressed.
Scaling = 1 if scaling is 2:1; 0 if scaling is 1:1 (see commands 0xE7 and 0xE6).
Enable = 1 if data reporting is enabled; 0 if data reporting is disabled (see commands 0xF5 and 0xF4).
Mode = 1 if remote mode is enabled; 0 if stream mode is enabled (see commands 0xF0 and 0xEA).

• 0xE8 (Set Resolution) - The mouse responds with "acknowledge" (0xFA) then reads one byte from the host and again responds with "acknowledge" (0xFA) then resets its movement counters. The byte read from the host determines the resolution as follows:

• 0xE7 (Set Scaling 2:1) - The mouse responds with "acknowledge" (0xFA) then enables 2:1 scaling.
• 0xE6 (Set Scaling 1:1) - The mouse responds with "acknowledge" (0xFA) then enables 1:1 scaling.

The only commands the standard PS/2 mouse will send to the host are "Resend" (FEh) and "Error" (FCh).

Initialization

The PS/2 mouse is normally detected/initialized only when the computer is booting up. That is, the mouse is not hot-pluggable and you must restart your computer whenever you add/remove a PS/2 mouse. Adding/removing the PS/2 mouse while the computer is running may physically damage some motherboards.

The initial detection of the PS/2 mouse occurrs during POST. If a mouse is detected, the BIOS will allow the operating system to configure/enable the mouse. Otherwise, it will inhibit communication on the mouse's bus. If you boot the computer with a mouse attached, then detach/reattach the mouse while in Windows, the OS may be able to detect the mouse was reattached. Testing this on Win98 SE, it seems to work about 50% of the time.

The following is the communication between my computer (running Win98 SE) and a standard PS/2 mouse during the boot process. It is fairly typical of how a PS/2 mouse is initialized and if you want to emulate a PS/2 mouse it must (at minimum) be able to support the following sequence of commands...

• Power-on Reset:
  Mouse: AA  Self-test passed
  Mouse: 00  Mouse ID
  Host:  FF  Reset command
  Mouse: FA  Acknowledge
  Mouse: AA  Self-test passed
  Mouse: 00  Mouse ID
  Host:  FF  Reset command
  Mouse: FA  Acknowledge
  Mouse: AA  Self-test passed
  Mouse: 00  Mouse ID
  Host:  FF  Reset command
  Mouse: FA  Acknowledge
  Mouse: AA  Self-test passed
  Mouse: 00  Mouse ID
  Host:  F3  Set Sample Rate   : Attempt to Enter Microsoft
  Mouse: FA  Acknowledge       : Scrolling Mouse mode
  Host:  C8  decimal 200       :
  Mouse: FA  Acknowledge       :
  Host:  F3  Set Sample Rate   :
  Mouse: FA  Acknowledge       :
  Host:  64  decimal 100       :
  Mouse: FA  Acknowledge       :
  Host:  F3  Set Sample Rate   :
  Mouse: FA  Acknowledge       :
  Host:  50  decimal 80        :
  Mouse: FA  Acknowledge       :
  Host:  F2  Read Device Type  :
  Mouse: FA  Acknowledge       :
  Mouse: 00  Mouse ID          : Response 03 if microsoft scrolling mouse
  Host:  F3  Set Sample Rate 
  Mouse: FA  Acknowledge
  Host:  0A  decimal 10
  Mouse: FA  Acknowledge
  Host:  F2  Read Device Type
  Mouse: FA  Acknowledge
  Mouse: 00  Mouse ID
  Host:  E8  Set resolution
  Mouse: FA  Acknowledge
  Host:  03  8 Counts/mm
  Mouse: FA  Acknowledge
  Host:  E6  Set Scaling 1:1
  Mouse: FA  Acknowledge
  Host:  F3  Set Sample Rate
  Mouse: FA  Acknowledge
  Host:  28  decimal 40
  Mouse: FA  Acknowledge
  Host:  F4  Enable
  Mouse: FA  Acknowledge
  Initialization complete...
• If I then press the Left Button...
  Mouse: 09 1 1 00001001; bit0 = Left button state; bit3 = always 1
  Mouse: 00 1 1 No X-movement
  Mouse: 00 1 1 No Y-movement
  ... and release the Left Button:
  Mouse: 08 0 1 00001000 bit0 = Left button state; bit3 = always 1
  Mouse: 00 1 1 No X-movement
  Mouse: 00 1 1 No Y-movement

from J.E. Davis posted by Peter Tiang

1. PC Mouse Systems

   Serial UART: 1200 baud, data=8,start=1,parity=none
   Mouse Protocol of Transmission
           bit:    7  6  5  4  3  2  1  0
   byte 1  (sync)  1  0  0  0  0  L  M  R      (0=depressed button)
   byte 2  (dX)    x7 x6 x5 x4 x3 x2 x1 x0     (bit 7 -> 0=pos,1=neg)
   byte 3  (dY)    y7 y6 y5 y4 y3 y2 y1 y0
   byte 4  (dX')   x7 x6 x5 x4 x3 x2 x1 x0
   byte 5  (dY')   y7 y6 y5 y4 y3 y2 y1 y0
   Notes:  - all bytes are two's complement binary
           - dX, dY  = relative moves after last transmission
           - dX',dY' = relative moves since dX, dY were transmitted
   
   

2. Microsoft Mouse

   Serial UART: 1200 baud, data=7,stop=1,parity=none
   Mouse Protocol of Transmission (normal mode)
           bit:    7  6  5  4  3  2  1  0
   byte 1  (sync)  0  1  L  R  y7 y6 x7 x6    (1=depressed button)
   byte 2  (dX)    0  0 x5 x4 x3 x2 x1 x0     (MSB-> 0=pos,1=neg)
   byte 3  (dY)    0  0 y5 y4 y3 y2 y1 y0
   Notes:  - all moves bytes are two's complement binary
             (you must collect all bits together)
   

Wheel Motion Sensors

Mechanical mice use a Quadrature Encoder position sensor attached to a shaft that rubs against the ball.

Jinxs' 16F84 4 button directional controller pluges in place of an MS Mouse

See also:

• http://www.thevaportrail.com/pr/07_PS2Mouse/ps2mouse.html
• http://www.computer-engineering.org/ps2protocol/
• http://www.embeddedlinks.com/chipdir/oth/mouse.txt
• http://www.4qd.co.uk/faq/meece.html
• http://www.krystal.com/nsfaq/Q.12.html
• http://www.hut.fi/~then/mytexts/mouse.html
• http://32.97.166.75/imouse/

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