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PmodPS/2™ Reference Manual 

 

 

Copyright Digilent, Inc. All rights reserved. 

Other product and company names mentioned may be trademarks of their respective owners.

 

Page 2 of 4 

 

Pin Number  Description 

Data 

Not Used 

Clock 

Not Used 

Ground 

VCC 

 

Table 1. Pin description table. 

 

Keyboard and Mouse Interface 

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. 

PS/2

Connector

Pin 1

Pin 5

Pin 6

Bottom-up

hole pattern

Pin Definitions

   Pin     Function

     1      Data
     2      Reserved
     3      GND
     4      Vdd
     5      Clock
     6      Reserved

1

5

3

2

4

6

Pin 2

T

CK

T

SU

Edge 0

Edge 10

CLK

DATA

T

HLD

T

CK

'1' stop bit

'0' start bit

 

Symbol 

Parameter 

Min 

Max 

Tck 

Clock time 

30us 

50us 

Tsu 

Data-to-clock setup time 

5us 

25us 

Thld 

Clock-to-data hold time 

5us 

25us 

 

Table 2. Bus timings. 

3.1  Keyboard 

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). 

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 

Summary of Contents for PmodPS/2

Page 1: ...y movement and key press will be received and addressed Naturally whether or not the key press will actually perform a function is dependent on the software but the system board will still receive all of the inputs 2 Interfacing with the Pmod The PmodPS 2 communicates with the host board via the GPIO protocol Both the keyboard and mouse will use a data and a clock line to communicate their informa...

Page 2: ... 2 Reserved 3 GND 4 Vdd 5 Clock 6 Reserved 1 5 3 2 4 6 Pin 2 TCK TSU Edge 0 Edge 10 CLK DATA THLD TCK 1 stop bit 0 start bit Symbol Parameter Min Max Tck Clock time 30us 50us Tsu Data to clock setup time 5us 25us Thld Clock to data hold time 5us 25us Table 2 Bus timings 3 1 Keyboard The keyboard uses open collector drivers so that either the keyboard or an attached host device can drive the two wi...

Page 3: ... N 31 M 3A 41 49 4A Shift 59 Alt 11 Space 29 Alt E0 11 Ctrl E0 14 F1 05 F2 06 F3 04 F4 0C F5 03 F6 0B F7 83 F8 0A F9 01 F10 09 F11 78 F12 07 E0 75 E0 74 E0 6B E0 72 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 clo...

Page 4: ...f 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 L R 0 1 XS YS XY YY P...

Page 5: ...Mouser Electronics Authorized Distributor Click to View Pricing Inventory Delivery Lifecycle Information Digilent 410 094P 410 094 ...

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