Unlike most of the consoles around at the PlayStation's conception, it has a relatively sophisticated shared serial bus for the controllers. This means that almost all the signals are wired together across the both controller and memory card ports, with one connection used to indicate which device the PlayStation is trying to talk to. All this requires some processing to occur in the controller itself, so the controllers have some form of microcontroller running internally to manage this intelligence.

            Looking at the plug
       -------------------------------
PIN 1- | o  o  o | o  o  o | o  o  o |
       \_____________________________/

It should also be noted that this is a bus of sorts. This means that the wires are all tied together except for the select lines which are unique for each of the two ports (though select lines are shared between the controller and memory card within each port). For the CLK, ATT, and CMD pins this does not matter as the PSX is always the originator. The DATA and ACK pins however can be driven from any one of four devices. To avoid contentions on these lines they are open collectors and can only be driven low.

All transmissions are eight bit serial LSB first. All timing in the PSX controller bus is syncronous to the falling edge of the clock. One byte of the transmissions will look kinda like this.

             |BIT 0|BIT 1|BIT 2|BIT 3|BIT 4|BIT 5|BIT 6|BIT 7|
  CLOCK -----___---___---___---___---___---___---___---___-----------

  DATA  -----000000111111222222333333444444555555666666777777--------
                *     *     *     *     *     *     *     *
  CMND  -----000000111111222222333333444444555555666666777777--------

  ACK   ----------------------------------------------------------__-
  

The logic level on the data lines is changed by the transmitting device on the falling edge of clock. This is then read by the receiving device on the leading edge (at the points marked *) allowing time for the signal to settle. After each COMMAND is recieved by a selected controller, that controller needs to pull ACK low for at least one clock tick. If a selected controller does not ACK the PSX will assume that there is no controller present.

When the PSX wants to read information from a controller it pulls that devices ATT line low and issues a start command (0x01). The Controller Will then reply with its ID (0x41=Digital, 0x23=NegCon, 0x73=Analogue Red LED, 0x53=Analogue Green LED). At the same time as the controller is sending this ID byte the PSX is transmitting 0x42 to request the data. Following this the COMMAND line goes idle and the controller transmits 0x5A to say “here comes the data”. This would look like this for a digital controller

  ATT    -______________________________________________________________
            |   Byte 1     |    |   Byte 2     |    |   Byte 3     |
  CLOCK  ---_-_-_-_-_-_-_-_-----_-_-_-_-_-_-_-_-----_-_-_-_-_-_-_-_-----
                 0xFF                0x41                0x5A 
  DATA   -------------------------__________--__----__--__----__--__----
                 0x01                0x42
  CMND   -----_____________-----__--________--__------------------------

  ACK    --------------------__-------------------__-----------------__-
  

After this command initiation proccess the controller then sends all its data bytes (in the case of a digital controller there is only two). After the last byte is sent ATT will go high and the controller does not need to ACK. The data transmision for a digital controller would look like this (where A0,A1,A2…B6,B7 are the data bits in the two bytes).

  ATT    _______________________________________-------
            |   Byte 4     |    |   Byte 5     |  
  CLOCK  ---_-_-_-_-_-_-_-_-----_-_-_-_-_-_-_-_--------

  DATA   ---D0D1D2D3D4D5D6D7----E0E1E2E3E4E5E6E7-------

  CMND   ----------------------------------------------
                                                  ***
  ACK    --------------------__------------------------

  NOTE: No ACK.
  

Below are five tables that show the actual bytes sent by the controllers

All Buttons are active low.

All Buttons are active low.

  BYTE    CMND    DATA
   01     0x01    idle
   02     0x42    0x73
   03     idle    0x5A    Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7
   04     idle    data    SLCT JOYR JOYL STRT UP   RGHT DOWN LEFT
   05     idle    data    L2   R2   L1   R1   /\   O    X    |_|
   06     idle    data    Right Joy 0x00 = Left  0xFF = Right
   07     idle    data    Right Joy 0x00 = Up    0xFF = Down
   08     idle    data    Left Joy  0x00 = Left  0xFF = Right
   09     idle    data    Left Joy  0x00 = Up    0xFF = Down

  All Buttons active low.

  BYTE    CMND    DATA
   01     0x01    idle
   02     0x42    0x53
   03     idle    0x5A    Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7
   04     idle    data                   STRT UP   RGHT DOWN LEFT
   05     idle    data    L2   L1   |_|  /\   R1   O    X    R2
   06     idle    data    Right Joy 0x00 = Left  0xFF = Right
   07     idle    data    Right Joy 0x00 = Up    0xFF = Down
   08     idle    data    Left Joy  0x00 = Left  0xFF = Right
   09     idle    data    Left Joy  0x00 = Up    0xFF = Down

  All Buttons active low.

(credit to T.Fujita http://www.keisei.tsukuba.ac.jp/~kashima/games/ps-e.txt)

  BYTE    CMND    DATA
   01     0x01    idle
   02     0x42    0x12
   03     idle    0x5A    Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7
   04     idle    0xFF
   05     idle    data         L    R
   06     idle    data    Delta Vertical
   07     idle    data    Delta Horizontal

  All Buttons active low.

This page substantially based on Andrew J McCubbin's page which has since disappeared from the net.

Commands sent by the PlayStation (within the first five bytes of a packet) tell the controller how it should be configured, and what data it should respond with. Because each controller port also shares its ATT/Select line with the memory card of the same port, commands at the beginning of each packet specify which device the console is addressing. Packets beginning with 0x01 address the controllers, while packets beginning with 0x81 address memory cards. It is important that controllers not respond to or acknowledge packets which begin with 0x81, otherwise conflicts will occur with memory cards on the same port.