User's Manual

9XTend™ OEM RF Module - Product Manual v2.x6x

API Operation - with Escape Characters (AP parameter = 2)

When this API mode is enabled (AP = 2), the UART data frame structure is defined as follows:

Figure 5-02. UART Data Frame Structure - with escape control characters

Escape characters. When sending or receiving a UART data frame, specific data values must be

escaped (flagged) so they do not interfere with the UART or UART data frame operation. To escape

an interfering data byte, insert 0x7D and follow it with the byte to be escaped XOR'd with 0x20.

Data bytes that need to be escaped:

 0x7E - Frame Delimiter

 0x7D - Escape

 0x11 - XON



0x13 - XOFF

Example - Raw UART Data Frame (before escaping interfering bytes):

0x7E 0x00 0x02 0x23 0x11 0xCB

0x11 needs to be escaped which results in the following frame:

0x7E 0x00 0x02 0x23 0x7D 0x31 0xCB

Note: In the above example, the length of the raw data (excluding the checksum) is 0x0002 and

the checksum of the non-escaped data (excluding frame delimiter and length) is calculated as:

0xFF - (0x23 + 0x11) = (0xFF - 0x34) = 0xCB.

Checksum

To test data integrity, a checksum is calculated and verified on non-escaped data.

To c

alculate: Not including frame delimiters and length, add all bytes keeping only the lowest 8

bits of the result and subtract from 0xFF.

To verify: Add all bytes (include checksum, but not the delimiter and length). If the checksum is

correct, the sum will equal 0xFF.

API Types

Frame data of the UART data frame forms an API-specific structure as follows:

Figure 5-03. UART Data Frame & API-specic Structure

The cmdID frame (API-identifier) indicates which API messages will be contained in the cmdData

frame (Identifier-specific data). Refer to the sections that follow for more information regarding

the supported API types. Note that multi-byte values are sent big endian.