API non-escaped (API 1) operation relies solely on the start delimiter and length bytes to differentiate API frames. If bytes in a packet are lost, the length

count will be off, and the next API frame (packet) will also be lost. API escaped (API 2) operation involves escaping character sequences in an API frame in

order to improve reliability, especially in noisy RF environments.

The basic frame structure of both API modes is the same, but in API escaped (API 2) mode, all bytes except for the start delimiter must be escaped if

needed. The following data bytes must be escaped in API 2 mode:

0x7E: Start delimiter

0x7D: Escape character

0x11: XON

0x13: XOFF

API 2 mode guarantees all the 0x7E bytes received are start delimiters: this character cannot be part of any of the other frame fields (length, data, or

checksum) since it must be escaped.

To escape a character:

1. Insert 0x7D, the escape character.

2. Append it with the byte to be escaped, XORed with 0x20.

In API 2 mode, the length field does not include any escape character in the frame and the checksum is calculated with non-escaped data.

Example: Escape an API frame

To express the following API non-escaped frame in API 2 mode:

Frame Data

Start Delimiter Length

Frame type Data

The 0x13 byte must be escaped:

01 00