Apple Desktop Bus Protocol (2021)
11 days ago
- #Input Devices
- #Vintage Computing
- #ADB Protocol
- Apple Desktop Bus (ADB) is a serial connection protocol designed for human input devices like keyboards and mice, allowing multiple devices to be chained on a single bus.
- The protocol features device addresses, up to 4 registers per device for data storage or behavior modification, and four host commands: Talk, Listen, SendReset, and Flush.
- Initial setup involves a reset signal and potential address reassignment to avoid collisions, especially when multiple devices of the same type are connected.
- Transactions are initiated by the host, with devices able to assert a service request (Srq) during the stop bit to indicate they need attention.
- Keyboards and mice have specific register structures for data, with keyboards supporting both Standard and Extended protocols for additional functionality like LED control and modifier key differentiation.
- Timings for signals like bit cells, attention, sync, and stop bits are critical for proper communication, with specific tolerances for host and device timings.