PmodPS/2™ Reference Manual
Copyright Digilent, Inc. All rights reserved.
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Page 4 of 4
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).
L
R
0
1 XS YS XY YY P
X0 X1 X2 X3 X4 X5 X6 X7 P
Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 P
1
0
1
0
0
1
1
Idle state
Start bit
Stop bit
Start bit
Mouse status byte
X direction byte
Y direction byte
Stop bit
Start bit
Stop bit
Idle state
4
Physical Dimensions
The pins on the pin header are spaced 100 mil apart. The PCB is 1 inch long on the sides parallel to the pins on the
pin header and 0.8 inches long on the sides perpendicular to the pin header.