Synaptics TouchPad Interfacing Guide

Synaptics TouchPad Interfacing Guide Second Edition
5.3. Power-on reset
The Synaptics TouchPad is able to respond to ADB bus traffic within 200ms of powerup.
The device’s ADB port is fully functional after this point for as long as power is
applied.
At power-up, the TouchPad mode byte is set to $00. The initial ADB address is 3, and
the initial handler ID is $01. Power-up settings are restored whenever a Global Reset
signal or SendReset command occurs on the ADB bus.
5.4. Command set
The Synaptics TouchPad emulates a standard ADB mouse. It supports the Cursor Device
Manager interface as well as the older 100- and 200-dpi interfaces. It also supports
extensions that allow the host to access the Synaptics TouchPad’s special features.
All ADB devices have four logical registers up to eight bytes in length. The Synaptics
TouchPad supports the usual ADB commands for accessing these registers:
• The “Talk” command reports the current contents of any of the four ADB registers.
• The “Listen” command stores a new value into one of the four registers.
• The “Flush” command clears any pending motion packet, but has no other effect on
the state of the device.
• The “SendReset” command and the “Global Reset” signal reset the device to its
power-up state.
The Synaptics TouchPad treats invalid command codes the same as “Flush” commands.
In the Synaptics TouchPad, the four ADB registers are assigned as follows:
ADB Register Length Contents
0 0–5 Current finger motion packet
1 8 CDM identification
2 8 Synaptics TouchPad mode bytes
3 2 ADB identification
Figure 5-4. ADB Registers
These registers are described in the sections below.
5.4.1. ADB Register 0
This register contains the current finger motion or position data. It has the special
property that it is empty (“Talk 0” does not respond) if there is no motion to report. The
host must poll Register 0 periodically to collect the motion data. The device asserts a
“Service Request” whenever Register 0 becomes full but the host is talking to a different
ADB device. The device continues to assert Service Requests until the host sends a
Copyright © 2001 Synaptics, Inc. 510-000080 - A §5.3 Page 66