PS/2 to Sun mouse converter

by Martin D. J. Rosenau

Abstract

The following text describes a circuit I developed that allows you to connect a PS/2 mouse to a Sun Microsystems workstation. It is mainly based on a 8051 compatible microcontroller. Special functions (such as mouse wheels) are ignored by the circuit and are ignored.

Warning

The device has been tested with my mouse and my computer. I cannot give you a warranty that it will work with your mouse and your computer. Under bad circumstances the device might damage your mouse or your computer. You use the circuit on your own risk !!!

Parts list

  • 1 Microcontroller, 8051 or MCS51 compatible (I use the Atmel 89S8252); minimum: 1k ROM, 64 bytes RAM
  • 1 (or 2) capacitor, 1uF
  • 3 (or 4) resistors, 1k
  • 1 quartz crystal or resonator (12 or 24 MHz)
  • 2 capacitors, value depending on crystal or resonator (30pF)
  • Sun mouse connector (Mini-Din-8, male)
  • PS/2 connector (Mini-DIN-6, female)
  • One button or switch (for reset)
  • wires, board, ... (what every circuit needs)
    Depending on the Microcontroller other resonator frequencies and other capacitors must be used.

    The sun mouse plug

    The sun mouse plug has the following pinout. Original sun mice have a plug with only 3 pins; 5 pins are missing. These missing pins should not be used:

    The Protocol

    Unlike "/dev/mouse" (that uses the 3 byte Sun protocol) the 5 byte Mouse Systems protocol is used on the hardware side. The signals coming from the mouse are the same a serial Mouse Systems mouse would send but the logic level is inverted TTL. This means a "0" is represented by +5V and a "1" by 0V. The following drawing shows one byte transmitted this way:

    The 5 bytes have the following meaning:
    Byte 1: 10000LMR
    Byte 2: X1
    Byte 3: Y1
    Byte 4: X2
    Byte 5: Y2
    The last 4 bytes are signed values that might have a value of 10000xxx, too, so there is no possibility to detect the first byte of the packet. On the other hand a value of 10000xxx would be such a fast mouse movement that such values never appear so 10000xxx can be seen as indication of the start of a new packet.
    The real X movement is (X1+X2) (positive=left). The circuit uses X2=constant=0. All movement data is transmitted over X1. The same is true for Y1/Y2 (positive=up).

    Schematics


    This schematics is based on another shematics developed by me that is used to connect PS/2 mice to the RS232 port.
    The pin numbers at the MCU are valid for the DIP 40 variant of the 89S8252. If you use another device please read the device manual for correct pin numbers.
    This schematics assumes that all port 3 pins are open-collector bidirectional I/O pins (that may have a pull-up resistor). The current version of the firmware assumes all pins to be in high- impedance mode (= HIGH) on power-on. You can even use different pins for input, output and interrupt (Ext #0, falling edge) if the source code is modified.
    You may use a soft reset button or not. If you do not use one you must either connect pin 13 to High or modify the firmware (normally pin 13 is connected to High using a pull-up resistor internally !). If you do not use a soft reset button you need a hard reset button that uses the Reset pin (pin 9). This variant requires a 4th resistor to avoid a shortcut of the capacitor.

    Firmware source code

    ; PS/2 to Sun mouse converter
; Needs an (extended ?) 8051
; Copyright (c) 2003 by Martin D. J. Rosenau
;
; Memory usage:
; 1Dh: Used by the PS/2 receiver
; 1Eh..1Fh: Used by the PS/2 transmitter
; 20h: Used by the serial routine
; 21h: Bit0: PS/2 bit received (cleared by other routines)
;      Bit1:
; 22h: First byte of a packet received
; 23h: First byte (button state) of the last packet translated
; 24h: Relative X movement
; 25h: Relative Y movement
; 26h..27h: Used by the main program
; 30h..33h: Serial send buffer
; 34h: Number of bytes in the serial buffer
;      If N>4 the last byte is repeated (N-3) times.
; 35h..38h: Used by the serial routines
; 39h: Byte received from PS/2 port
; 3Ah..3Dh: Used by the PS/2 receiver
; 3Eh..3Fh: Used by the PS/2 transmitter
;
; Ports:
; 3.1 - Mouse data (output)
; 3.2/INT0 - PS/2 clock (TTL; IN&OUT)
; 3.3 - LOW = Reset
; 3.7 - PS/2 data (TTL; IN&OUT)
;

; Definition of the port bits
; You may change the pins; PS/2 clock
; must be the same pin as INT0 !
PS2IN       bit 0B7h
PS2OUT      bit 0B7h
MSRESET     bit 0B3h
PS2CLOCKIN  bit 0B2h
PS2CLOCKOUT bit 0B2h
SERIALOUT   bit 0B1h

; Some crystal frequency dependent values
; You must change these values when
; using a different crystal !
; about MHz*(2.5) -> 60 for 24 MHz
TIME1       equ 60
; 100h-(MHz*(2.15)) -> 0CCh for 24 MHz
TIME2       equ 0CCh

; Header
  sjmp start
  org 3
  ljmp onclockin
  org 1Bh
  ljmp ontimer1
  org 40h

; The start of it...
start:
  ; Wait until an initialize
  ; signal is received...
  clr SERIALOUT
  clr 9
  mov 0A8h,#0
  mov C,MSRESET
  jnc start
  ; Initialize the serial port
  acall serinit
  mov 34h,#0
  ; Clear the PS/2 port and enable it
  clr 8
  setb 88h
  mov 3Ah,#0
  mov 23h,#0
  mov 24h,#0
  mov 25h,#0
  mov 1Dh,#0
  ; Send initialition data to the PS/2 mouse
  mov A,#0F4h
  acall ps2send
  acall ps2read
  mov A,#0E7h
  acall ps2send
  acall ps2read
  mov A,#0E8h
  acall ps2send
  acall ps2read
  mov A,#1
  acall ps2send
  acall ps2read
  setb 0A8h
  setb 9

  ; The working loop
  ; Restart the program any time RTS goes low.
waitfirst:
  ; Wait while a serial transmission is done
  mov A,34h
  jnz waitfirst
  ; "Reset" detected
  mov C,MSRESET
  jnc start
  ; Did the mouse position or buttons change ?
  mov A,24h
  jnz mousechanged
  mov A,25h
  jnz mousechanged
  mov A,22h
  xrl A,23h
  anl A,#7
  jz waitfirst
mousechanged:
  ; The mouse position changed, so a packet must be sent...
  mov 26h,24h
  mov 24h,#0
  mov 27h,25h
  mov 25h,#0
  mov 23h,22h
  ; Buttons
  mov A,#080h
  mov C,18h
  mov 0E2h,C
  mov C,19h
  mov 0E0h,C
  mov C,1Ah
  mov 0E1h,C
  xrl A,#7
  ; Finish the packet
  mov 30h,A
  mov A,26h
;  anl A,#7Fh
  mov 31h,A
  mov A,27h
;  anl A,#7Fh
  mov 32h,A
  mov 33h,#0
  mov 34h,#5
  ; Restart
  sjmp waitfirst

; PS/2 clock line detected
onclockin:
  mov 3Bh,A
  mov 3Ch,0D0h
  mov A,3Ah
  jnz notfirstps2
  ; It is a start bit => MUST be 0 !
  mov C,PS2IN
  jc onclockend
  mov 3Ah,#10
  sjmp onclockend

notfirstps2:
  dec 3Ah
  dec A
  jnz notstopbit
  ; It is a stop bit
  mov C,PS2IN
  jnc onclockend
  mov 39h,3Dh
  setb 8
  mov C,9
  jc onautops2
  sjmp onclockend
notstopbit:
  dec A
  ; Ignore parity
  jz onclockend
  mov A,3Dh
  mov C,PS2IN
  rrc A
  mov 3Dh,A
onclockend:
  mov A,3Bh
  mov 0D0h,3Ch
  reti
onautops2:
  ; Automatically process PS/2 data
  mov A,1Dh
  dec A
  jnz isnot2
  ; 2nd byte
  inc 1Dh
  mov A,39h
  add A,24h
  mov 24h,A
  sjmp onclockend
isnot2:
  ; 3rd byte
  dec A
  jnz isnot3
  mov 1Dh,#0
  mov A,39h
  add A,25h
  mov 25h,A
  sjmp onclockend
isnot3:
  ; 1st byte
  mov A,39h
  mov C,0E3h
  jnc onclockend
  mov 22h,A
  mov 1Dh,#1
  sjmp onclockend

; Initialize the serial routine
serinit:
  clr SERIALOUT
  mov 0A8h,#0
  mov 89h,#0
  mov 8Dh,0
  mov 34h,#0
  mov 35h,#0
  setb 8Eh
  mov 0A8h,#88h
  ret

; Read a single byte from the PS/2 port
ps2read:
  setb 0A8h
  mov C,8
  jnc ps2read
  mov A,39h
  clr 8
  ret

; Send a byte over the PS/2 port
; Disables the external interrupt.
ps2send:
  clr 0A8h
  mov 1Eh,A
  mov 1Fh,A
  ; Wait some time
  mov A,128
ps2waitpre:
  dec A
  jnz ps2waitpre
  ; Inhibit
  clr PS2CLOCKOUT
  mov A,#TIME1
ps2dowait:
  dec A
  jnz ps2dowait
  setb PS2CLOCKOUT
  clr PS2OUT
  ; Send all bits
  mov 3Fh,#8
nextbitps2:
  mov A,1Fh
  rrc A
  mov 1Fh,A
  acall sendps2bit
  dec 3Fh
  mov A,3Fh
  jnz nextbitps2
  ; Send the parity bit
  mov A,1Eh
  xrl A,#1
  mov C,0D0h
  acall sendps2bit
  ; Send the stop bit and receive the ACK bit
  setb C
  acall sendps2bit
  setb C
  acall sendps2bit
ackwait:
  mov C,PS2IN
  jnc ackwait
  ret

; Send a bit (C) to the PS/2 port
sendps2bit:
  mov 3Eh,0D0h
sendps21:
  mov C,PS2CLOCKIN
  jc sendps21
  mov 0D0h,3Eh
  mov PS2OUT,C
sendps22:
  mov C,PS2CLOCKIN
  jnc sendps22
  mov 0D0h,3Eh
  ret

; Timer 1 interrupt routine: Serial port
; emulation (the hardware UART is no used)
ontimer1:
  ; restart the timer
  mov 8Dh,#TIME2
  ; save the accumulator
  mov 37h,A
  mov 38h,0D0h
  ; is a byte currently being sent ?
  mov A,35h
  jnz duringsend
  ; No bytes is currently being sent
  ; Start one ?
  mov A,34h
  jnz beginsend
  ; Exit the interrupt
ontimer1end:
  mov A,37h
  mov 0D0h,38h
  reti
beginsend:
  ; begin sending a byte
  mov 20h,30h
  mov 30h,31h
  mov 31h,32h
  mov 32h,33h
  dec 34h
  setb SERIALOUT
  ; Still 9 bits to be sent (including
  ; 1 stop bit)
  mov 35h,#9
  sjmp ontimer1end
duringsend:
  ; What to do while transmitting a byte...
  dec 35h
  mov A,20h
  setb C
  rrc A
  cpl C
  mov SERIALOUT,C
  mov 20h,A
  sjmp ontimer1end

end

    Compiled firmware

    Here is the compiled firmware in HEX file format. The program is compiled for the following configuration:
  • Crystal frequency: 24 MHz
  • Device: Atmel 89S8252 (should work on most other devices, too)
  • Port 3.1 is used as Sun mouse output
  • Port 3.2 is used as bidirectional PS/2 clock port and is the falling-edge interrupt #0 pin
  • Port 3.3 is the negated Reset input
  • Port 3.7 is used as bidirectional PS/2 data port 
    :02000000803E40
:030003000200C830
:03001B0002019748
:10004000C2B1C20975A800A2B350F53128753400B9
:10005000C208D288753A0075230075240075250002
:10006000751D0074F4314A313F74E7314A313F74F1
:10007000E8314A313F7401314A313FD2A8D209E513
:100080003470FCA2B350B9E524700CE5257008E586
:10009000226523540760E8852426752400852527DA
:1000A0007525008522237480A21892E2A21992E09D
:1000B000A21A92E16407F530E526F531E527F5321D
:1000C00075330075340580B7F53B85D03CE53A7053
:1000D00009A2B74023753A0A801E153A14700FA280
:1000E000B75015853D39D208A2094012800A146024
:1000F00007E53DA2B713F53DE53B853CD032E51D54
:1001000014700A051DE5392524F52480EB14700BC5
:10011000751D00E5392525F52580DDE539A2E3507B
:10012000D7F522751D0180D0C2B175A80075890070
:1001300085008D753400753500D28E75A88822D261
:10014000A8A20850FAE539C20822C2A8F51EF51F78
:10015000E5801470FDC2B2743C1470FDD2B2C2B717
:10016000753F08E51F13F51F3183153FE53F70F319
:10017000E51E6401A2D03183D33183D33183A2B78A
:1001800050FC2285D03EA2B240FC853ED092B7A260
:10019000B250FC853ED022758DCCF53785D038E540
:1001A00035701FE5347006E5378538D0328530204C
:1001B0008531308532318533321534D2B175350908
:0F01C00080E51535E520D313B392B1F52080D833
:00000001FF

    Usage

    After connecting the mouse (and possibly after power-up) the reset button must be pressed !
    Copyright © 2003 by Martin D. J. Rosenau