Editing Apple Desktop Bus (section)

== Device Addressing and Enumeration ==

=== Default Addresses ===
{| class="wikitable" style="width:60%; text-align:center;"
|+'''ADB Default Device Addresses'''
! Address !! Device Type !! Notes
|-
| $0 || Reserved || SendReset command
|-
| $1 || Security dongles || Copy protection devices
|-
| $2 || Keyboards || All keyboards default to this
|-
| $3 || Mice/Pointing devices || Mice, trackballs, trackpads
|-
| $4 || Graphics tablets || Absolute positioning devices
|-
| $5 || Reserved || Vendor-specific
|-
| $6 || Reserved || Vendor-specific
|-
| $7 || Reserved || Vendor-specific
|-
| $8-$E || Relocated devices || Collision resolution addresses
|-
| $F || Reserved || Global polling address
|}

=== Enumeration Process ===
The ADB Manager performs device enumeration at startup:

# '''Reset:''' SendReset command clears all devices
# '''Discovery:''' Poll each default address with Talk Register 3
# '''Collision Detection:''' If multiple devices respond:
#* Devices detecting collision stop transmitting
#* Non-colliding device completes transmission
# '''Address Resolution:'''
#* Send Listen Register 3 with new address ($8-$E) and handler ID $FE
#* Only non-colliding device moves to new address
#* Repeat until all devices have unique addresses
# '''Verification::''' Poll new addresses to confirm relocation
# '''Handler Installation::''' Install appropriate device drivers

=== Service Requests ===
Devices can request service by:
# Pulling bus low during stop bit of any transaction (65-300μs)
# Host detects extended stop bit as Service Request (SRQ)
# Host polls all devices' Register 0 sequentially
# Device with data becomes new active device
# Active device is polled continuously until another SRQ