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® Digilent PmodPS/2™ Module Board Reference Manual Revision: August 3, 2006 www .d ig ilen tinc .c om 215 E Main Suite D | Pullman, WA 99163 (509) 334 6306 Voice and Fax Overview The Digilent PmodPS/2 module board allows a Digilent system board to send and receive signals from a PS/2-style keyboard or mouse. The PS/2 is designed for use with either a Digilent programmable logic system board or a Digilent embedded control system board. Features include: • • a 6-pin header for connection to a system board PS/2 connector for a keyboard or mouse power routing jumpers Functional Description The PS/2 has a 6-pin header for easy connection to a Digilent system board. Most of Digilent’s programmable logic system boards (like the Nexys™ or Basys™ boards) or Digilent’s embedded control boards (like the Cerebot™) have 6-pin connectors that allow direct connection of the PS/2. To connect the PS/2 to some older Digilent system boards, a Digilent Modular Interface Board (MIB) and a 6-pin cable may be needed. The MIB plugs into the system board, and the cable connects the MIB to the PS/2. Power to the keyboard or mouse can be provided from the system board or an external power supply. To power the keyboard or mouse from the system board, set the shorting block on jumper JP2 to the VB position. To power the keyboard or mouse from an external power supply, set the shorting bock on JP2 to the VE position and attach the external power supply to JP1. The external supply voltage is attached to the VE pin of JP1 and the ground Doc: 502-094 P2 Data GND J1 Connection • VCC P4 CLK PS/2 Connector GND VCC JP1 JP2 VCC GND External Power PmodPS/2 Circuit Diagram for the external power supply is attached to the GND pin of JP1. NOTE: Some keyboards and mice can operate with a 3.3V power supply but some require a 5V power supply. Be careful to observe the correct polarity when connecting an external power supply to JP1 and do not use an external power supply voltage greater than 5V. page 1 of 4 Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. PS/2 Reference Manual Digilent, Inc. Keyboard Keyboard and Mouse Interface Pin 2 1 3 5 2 4 6 Pin 1 Pin Definitions Pin 5 Pin 1 2 3 4 5 6 Pin 6 Bottom-up hole pattern PS/2 Connector Function Data Reserved GND Vdd Clock Reserved The keyboard and mouse both use identical signal timings. Both use 11-bit words that include a start, stop, and odd parity bit, but the data packets are organized differently, and the keyboard interface allows bi-directional data transfers (so the host device can illuminate state LEDs on the keyboard). Bus timings are shown below. The clock and data signals are only driven when data transfers occur, and otherwise they are held in the “idle” state at logic ‘1’. The timings define signal requirements for mouse-to-host communications and bi-directional keyboard communications. TCK TCK Edge 10 Edge 0 THLD ED DATA '0' start bit Symbol PS/2-style keyboards use scan codes to communicate key-press data (nearly all keyboards in use today are PS/2 style). Each key has a single, unique scan code that is sent whenever the corresponding key is pressed. If the key is pressed and held, the scan code will be sent repeatedly once every 100ms or so. When a key is released, an “F0” key-up code is sent, followed by the scan code of the released key. If a key can be “shifted” to produce a new character (like a capital letter), then a shift character is sent in addition to the original scan code, and the host device must determine which character to use. Some keys, called extended keys, send an “E0” ahead of the scan code (and they may send more than one scan code). When an extended key is released, an “E0 F0” key-up code is sent, followed by the scan code. Scan codes for most keys are shown in the keyboard diagram below. A host device can also send data to the keyboard. Below is a short list of some oft-used commands. CLK TSU The keyboard uses open-collector drivers so that either the keyboard or an attached host device can drive the two-wire bus (if the host device will not send data to the keyboard, then the host can use simple input-only ports). '1' stop bit Parameter Min Max TCK Clock time 30us 50us TSU Data-to-clock setup time 5us 25us THLD Clock-to-data hold time 5us 25us EE F3 FE FF www.digilentinc.com Set Num Lock, Caps Lock, and Scroll Lock LEDs. After receiving an “ED”, the keyboard returns an “FA”, then the host sends a byte to set LED status. Bit 0 sets Scroll Lock, bit 1 sets Num Lock; and Bit 2 sets Caps lock. Bits 3 to 7 are ignored. Echo. Upon receiving an echo command, the keyboard replies with “EE”. Set scan code repeat rate. The keyboard acknowledges receipt of an “F3” by returning an “FA”, after which the host sends a second byte to set the repeat rate. Resend. Upon receiving FE, the keyboard resends the last scan code sent. Reset. Resets the keyboard. page 2 of 4 Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. PS/2 Reference Manual ESC 76 `~ 0E 1! 16 TAB 0D Caps Lock 58 Shift 12 Digilent, Inc. F1 05 F2 06 F3 04 F4 0C 2@ 1E 3# 26 4$ 25 5% 2E Q 15 W 1D A 1C S 1B Z 1Z Ctrl 14 E 24 D 23 X 22 Alt 11 R 2D F5 03 6^ 36 T 2C F 2B C 21 F6 0B V 2A 7& 3D Y 35 G 34 8* 3E U 3C H 33 B 32 Space 29 The keyboard sends data to the host in 11-bit words that contain a ‘0’ start bit, followed by 8bits of scan code (LSB first), followed by an odd parity bit and terminated with a ‘1’ stop bit. The keyboard generates 11 clock transitions (at around 20 - 30KHz) when the data is sent, and data is valid on the falling edge of the clock. Mouse The mouse outputs a clock and data signal when it is moved, otherwise these signals remain at logic ‘1’. Each time the mouse is moved, three 11-bit words are sent from the mouse to the host device. Each of the 11-bit words contains a ‘0’ start bit, followed by 8 bits of data (LSB first), followed by an odd parity bit, and terminated with a ‘1’ stop bit. Thus, F8 0A 9( 46 I 43 J 3B N 31 The keyboard sends data to the host only when both the data and clock lines are high (or idle). Since the host is the “bus master”, the keyboard checks to see whether the host is sending data before driving the bus. To facilitate this, the clock line can be used as a “clear to send” signal. If the host pulls the clock line low, the keyboard will not send any data until the clock is released. www.digilentinc.com F7 83 0) 45 O 44 K 42 M 3A F9 01 -_ 4E P 4D L 4B ,< 41 F10 09 =+ 55 [{ 54 ;: 4C >. 49 /? 4A Alt E0 11 F11 78 F12 07 E0 75 BackSpace 66 E0 74 ]} 5B '" 52 \| 5D E0 6B Enter 5A E0 72 Shift 59 Ctrl E0 14 each data transmission contains 33 bits, where bits 0, 11, and 22 are ‘0’ start bits, and bits 11, 21, and 33 are ‘1’ stop bits. The three 8-bit data fields contain movement data as shown below. Data is valid at the falling edge of the clock, and the clock period is 20 to 30KHz. The mouse assumes a relative coordinate system wherein moving the mouse to the right generates a positive number in the X field, and moving to the left generates a negative number. Likewise, moving the mouse up generates a positive number in the Y field, and moving down represents a negative number (the XS and YS bits in the status byte are the sign bits – a ‘1’ indicates a negative number). The magnitude of the X and Y numbers represent the rate of mouse movement – the larger the number, the faster the mouse is moving (the XV and YV bits in the status byte are movement overflow indicators – a ‘1’ means overflow has occurred). If the mouse moves continuously, the 33-bit transmissions are repeated every 50ms or so. The L and R fields in the status byte indicate Left and Right button presses (a ‘1’ indicates the button is being pressed). page 3 of 4 Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. PS/2 Reference Manual Digilent, Inc. Mouse status byte 1 0 Idle state X direction byte L R 0 1 XS YS XY YY P 1 Start bit Stop bit Y direction byte 0 X0 X1 X2 X3 X4 X5 X6 X7 P 1 Start bit Stop bit 0 Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 P 1 Start bit Stop bit Idle state For more information see www.digilentinc.com. www.digilentinc.com page 4 of 4 Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Digilent: 410-267P