From Wikipedia, the free encyclopedia
Jump to navigation Jump to search

KISS (Keep It Simple, Stupid[1]) is a protocol for communicating with a serial terminal node controller (TNC) device used for amateur radio. This allows the TNC to combine more features into a single device and standardizes communications. KISS was developed by Mike Cheponis and Phil Karn to allow transmission of AX.25 packet radio frames containing IP packets over an asynchronous serial link, for use with the KA9Q NOS program.[1]


The KISS protocol is designed to be easy to implement in simple embedded devices, which are capable of asynchronous serial communications. While it allows arbitrary data to be transferred, there is no support for flow control or error handling.

Back-to-back FEND codes should not be interpreted as empty frames. Instead, all but the last FEND code should be discarded. This can be used for synchronization.

If the FEND or FESC codes appear in the data to be transferred, they need to be escaped. The FEND code is then sent as FESC, TFEND and the FESC is then sent as FESC, TFESC.

Special characters[edit]

Hex value Abbreviation Description
0xC0 FEND Frame End
0xDB FESC Frame Escape
0xDC TFEND Transposed Frame End
0xDD TFESC Transposed Frame Escape

Command codes[edit]

Any of these codes may be sent from the host to the TNC, but only the "Data frame" code should be sent from the TNC to the host. "In multi-port TNCs, the upper 4 bits of the type indicator byte can specify one of up to sixteen ports."[1]

Hex value Name Bytes Description
0x00 Data frame Varies This frame contains data that should be sent out of the TNC. The maximum number of bytes is determined by the amount of memory in the TNC.
0x01 TX DELAY 1 The amount of time to wait between keying the transmitter and beginning to send data (in 10 ms units).
0x02 P 1 The persistence parameter. Persistence=Data*256-1. Used for CSMA.
0x03 SlotTime 1 Slot time in 10 ms units. Used for CSMA.
0x04 TXtail 1 The length of time to keep the transmitter keyed after sending the data (in 10 ms units).
0x05 FullDuplex 1 0 means half duplex, anything else means full duplex.
0x06 SetHardware Varies Device dependent.
0xFF Return 0 Exit KISS mode. This applies to all ports and requires a port code of 0xF.

Packet format[edit]

Begin Command Data0..DataN End
FEND High nibble – Port Index
Low nibble – Command

Send the characters "TEST" out of TNC port 0[edit]

C0 00 54 45 53 54 C0

Send the characters "Hello" out of TNC port 5[edit]

C0 50 48 65 6C 6C 6F C0

Send the bytes 0xC0, 0xDB out of TNC port 0[edit]

C0 00 DB DC DB DD C0

Exit KISS mode[edit]

C0 FF C0

Common uses[edit]


See also[edit]


  1. ^ a b c Mike Chepponis, K3MC; Phil Karn, KA9Q (1987). The KISS TNC: A simple Host-to-TNC communications protocol. ARRL 6th Computer Networking Conference. Redondo Beach CA.
  2. ^ "6PACK a "real time" PC to TNC protocol". Retrieved 2012-04-08.

External links[edit]