TNC LEDs Technical Seminar – Dec. 05/98
By Lane, VE7IHL
Introduction
This technical seminar will teach you what the meaning of each of a typical TNC's front panel LED's are showing you. These front panel LED's actual can operate in one of two modes. Normal or native TNC mode, and in KISS mode. KISS mode is used by PC packet software that requires more AX.25 features than is provided by the TNC's firmware operating in native mode. BBS programs and various types of packet Node switch software programs typically use this. (Like BPQ)
Note that some TNCs like the Kantronics KPC-3(+) can turn off their entire front panel LED's by a software command. This is usually done to save power when running off internal batteries.
TNC LED's That Don't Change with different TNC modes
The following list of TNC LED's do not change their purpose, even if the TNC is operating in different modes:
| LED: | DESCRIPTION: |
| Power or PWR | Always on when TNC is powered up |
| Xmit or PTT | Indicates when the radio is keyed up and transmitting |
| Rcv or DCD | Indicates when the TNC is receiving data from the radio |
TNC LED's Operation in Normal Mode
The following list of TNC LED's shows their purpose when running in Normal operating mode.
| LED: | DESCRIPTION: |
| CON | When lit, indicates that you have a packet 'connection' to another ax.25 station on the current packet stream. |
| STA | When lit, indicates that there is at least one packet that has not yet been acknowledged by the remote ax.25 station |
When lit, there is a packet connection to your TNC's internal mailbox. When this LED is blinking this means that their is a message waiting for you in the TNC's internal mailbox. |
TNC LED's Operation in KISS Mode
The following list of TNC LED's shows their purpose when running in KISS operating mode.
| LED: | DESCRIPTION: |
| CON | When lit, indicates that the TNC is sending packet receive data down the RS-232 serial port to the computer. This only lights briefly, and you will notice that the DCD LED will light briefly first. If the DCD LED flashes, but the CON LED does not, then the TNC has failed to decode the entire ax.25 data packet. This usually indicates a poorly received radio signal. |
| STA | When lit, indicates that the computer is sending transmit data down the RS-232 serial port to the TNC. This only lights briefly, and you will notice that the XMIT (or PTT) LED will light shortly after the STA LED. There should normally be a noticeable delay between the STA LED and the PTT LED. If not, you have your TNC set to aggressive. Check your persist settings. |
When lit, this can indicate that the TNC has lost power previously. It can be cleared by forcing the TNC out of KISS mode. This only applies to some TNCs, such as the AEA PK-96. |