Data Packet Format; Coding Method; Packet Types; Manchester Coding - Motorola M68HC08 Designer Reference Manual

NOTE:

5.3 Data Packet Format

5.3.1 Coding Method

5.3.2 Packet Types

High Data Rate Wireless USB Optical Mouse Solution
MOTOROLA
Freescale Semiconductor, Inc.
activity. If still no activity happens for 10 minutes, the activities are monitored
every 500 milliseconds.
Any XY movement will cause the mouse to enter high current stage. At this
stage, the sensor is powered on and XY movement is continually monitored.
The Z movement and button activities are still monitored every millisecond. If
no XY movement happens for 5 seconds, it then enters power saving stage.
Except for the 1 millisecond timer tick, all of the above mentioned timings can
be configured by changing their constant values.
A data packet consists of a start field, a data field, and a checksum field.
Except for the start field, both the data and the checksum fields are encoded
by using the Manchester Coding method. That is, a logic '0' is represented by
two equal times 'T' of a logic high or a logic low and vice verse for a logic '1'. An
additional '0' is added to the end of each byte of these two fields as stop bits.
Refer to Figure 5-3.
Figure 5-3. Manchester Coding
The order of transmission will be from least significant bit (LSB) to most
significant bit (MSB). For example, bit 0 will be transmitted first.
The basic time of each logic level toggle is 104 µs(T). Therefore, each bit in the
data and checksum fields will be a 2T period according to the Manchester
Coding.
There are two types of packets:
• X-Y displacements packet
• Button status and Z displacement packet
As the header patterns between these two packet types are different, the
receiver will not interpret a X-Y displacement packet as a Z and button status
packet or vice versa.
Mouse Transmitter Firmware
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"0"
(2T PERIOD) (2T PERIOD)
Mouse Transmitter Firmware
Data Packet Format
"1"
DRM055
23