Introduction

Messages are transferred between communication layers as Protocol Data Units (PDUs). The information stays the same, but the PDU is represented in different ways in different layers.

The zForce AIR sensor uses Abstract Syntax Notation One (ASN.1) objects to represent the information in the presentation layer. The Distinguished Encoding Rules (DER) are used to serialize the message into a binary representation for transfer via the transport layer. The bytes of the encoded message follow each other without any explicit delimiters and the integrity of the data is therefore of highest importance.

ASN.1 is a standardized way (ISO/IEC 8824) to describe data regardless of language implementation, hardware and operation system.

Transport Layer

The following transport interfaces are supported:

• I2C: The sensor's I2C implementation has a certain byte sequence and a signaling system to ensure stability. The sensor takes the role of an I2C slave and has the I2C address 0x50. For more information, refer to I2C Transport.
• USB HID Touch Digitizer: the sensor can be used as a standard HID Touch Digitizer to report touch data to the OS. For more information, refer to USB HID Transport. 
• USB RAW HID: the sensor uses HID Get and Set Feature Reports as a pipe to read and write. For more information, refer to USB HID Transport. 

Presentation Layer

For more information, refer to Presentation Layer (ASN.1).