22
Bit 7
Bit 0
Byte 0
Y
Overflow
X Overflow Y sign
X sign
Always 1
Middle
Button
Right
button
Left button
Byte 1
X
X
X
X
X
X
X
X
Byte 2
Y
Y
Y
Y
Y
Y
Y
Y
Byte 3
Wheel*
Wheel*
Wheel*
Wheel*
Wheel*
Wheel*
Wheel*
Wheel*
Start Bit
(Always 0)
Data Bit
0
Data Bit
1
Data Bit
2
Data Bit
3
Data Bit
4
Data Bit
5
Data Bit
6
Data Bit
7
Odd Parity
Bit
Stop Bit
(Always 1)
After the following sequence of commands, the wheel report format is enabled.
0xF3, 0xC8
Set Sampling Rate 200 per second
0xF3, 0x64
Set Sampling Rate 100 per second
0xF3, 0x32
Set Sampling Rate 50 per second
0xF2, 0x03
Read Device Type returns a value of 0x03
After the Read Device Type command returns 0x03 to indicate that this is a Microsoft compatible
three button-wheel mouse, the wheel report format is enabled. After this initialization sequence,
the PS/2 wheel reporting format is enabled. The fourth byte represents the wheel data. This byte
is assigned 0x01 for forward wheel movement and 0xFF for backward wheel movement. When the
wheel is idle, this value is 0x00.
The PS2 data transmission according to the PS/2 Hardware Interface Technical Reference
including eleven bits for each byte sent. The bits are sent in the following order with data valid
on the falling edge of the clock. See the PS/2 Hardware Interface Technical Reference manual for
timing information.
