1. Communication Protocol Overview

· Serial Communication: The microcontroller uses a serial communication protocol.
· Master/Slave: The microcontroller operates in a master/slave configuration, where an external host (e.g., a microcontroller) acts as the master and the AT42QT1111 is the slave.
· SPI-like: The protocol is described as similar to SPI (Serial Peripheral Interface), but with specific command structures and data handling.

2. Key Communication Types

· Report Requests: Used by the host to request status information from the AT42QT1111.
* The Host sends a command followed by Null bytes.
* The AT42QT1111 responds with the requested data on the next byte.
· Set Instructions: Used by the host to send configuration settings to the AT42QT1111.
* The Host sends a "Set" command and associated data.
* The AT42QT1111 responds with the same command received and then a "Idle" response.
* The data is *not* immediately applied until the entire transmission is complete and validated.
· Get Instructions: Used by the host to read configuration settings from the AT42QT1111.
* The Host sends a "Get" command.
* The AT42QT1111 responds with the requested data in the next byte.

3. Command Structure & Data

· Commands: Specific numerical codes (e.g., 0x95, 0xC1, 0xD5) represent different commands like "Set," "Report," or "Get."
· Data Bytes: These follow commands and contain information (e.g., settings, status reports).
· Null Bytes (0x00): Used as placeholders in several communication sequences.
· "Idle" Response (0x55): This signifies that the AT42QT1111 is ready to interpret the next byte as a command.

4. CRC (Cyclic Redundancy Check)

· Optional: CRC is an optional but recommended mechanism for error detection.
· Calculation: The Host and the AT42QT1111 calculate CRC values based on transmitted data.
· Verification: The receiving device verifies the received CRC against its own calculation. If there's a mismatch, the communication is considered invalid.
· Extended Transmission: When CRC is enabled, the total number of bytes exchanged for each command sequence increases.

5. Sequence Examples

· Positive Recalibration Delay Set Instruction (CRC Disabled): `0x95 0x0C` (Host sends set command and associated data).
· All Keys Report (CRC Enabled): `0xC1 (CRC) 0x00 0x00 0x00 0x00 (Key Status Bytes) (Report CRC)`

6. Key Considerations

· Timing: The document doesn't explicitly define timing requirements (clock speeds, data rates, etc.) but assumes a synchronous operation. Precise timing would be crucial for reliable communication.
· Memory Map: The AT42QT1111's memory map is critical; address codes are used to target specific settings and data locations.