3.1.2.1 Telegram Structure
The system supports the transmission and reception of a wide variety of telegrams and protocols. Generally, the system can receive arbitrary telegrams. However, the chip contains designated hardware and software blocks that support the telegram structure illustrated in the following figure. Using this structure or parts of it will improve the sensitivity and the robustness of the broadcast.
| Desync | Preamble | Data Payload | Checksum | Stop Sequence | |
| WUP | SFID | ||||
Desync
The de-synchronization is usually a coding violation with a length of several symbols that are supposed to provoke a defined restart of the receiver. The use of a de-synchronization leads to more deterministic receiver behavior, reducing the required preamble length. This can be favorable in timing-critical and energy-critical applications.
Preamble
The preamble is a pattern that is sent before
the actual data payload to synchronize the receiver and provide the starting point of
the payload. Microchip recommends a regular symbol pattern (example,
1-0-1-0...) for
synchronization, Wake-Up Pattern (WUP), sometimes also called pre-burst, while a unique,
well-defined pattern of up to 32 symbols is required to mark the start of the data
payload (Start Frame Identifier (SFID) or Start bit). In polling scenarios, the WUP can
be tens or hundreds of ms long.
Data Payload
The data payload contains the actual information content of the telegram. It can be NRZ or Manchester-coded. The length of the payload is application-dependent, typically 1 to 64 bytes.
Checksum
The system calculates the checksum across the data payload to verify the received data. A typical example is an 8-bit CRC checksum.
Stop Sequence
The stop sequence is a short data pattern (typically, 2 to 6 symbols) to mark the end of the telegram. Use a coding violation to prevent additional (non-deterministic) data from being received.