Updated Protocol and compatibility (markdown)

Protocol-and-compatibility.md

@@ -17,4 +17,7 @@ At the link level, APRS uses the AX.25 protocol, as defined in AmateurPacket-Rad
 - **Control Field** — This field is set to 0x03 (UI-frame).
 - **Protocol ID** — This field is set to 0xf0 (no layer 3 protocol).
 - Information Field — This field contains more APRS data. The first character of this field is the APRS Data Type Identifier that specifies the nature of the data that follows.
-- Frame Check Sequence — The FCS is a sequence of 16 bits used for checking the integrity of a received frame.
+- Frame Check Sequence — The FCS is a sequence of 16 bits used for checking the integrity of a received frame.
+
+# TNC2 protocol
+TNC2 protocol does not use KISS, it sends text based APRS messages, multiple messages are separated by using new line character `\n`.