KISS TNC over UART - is possible?

[UT4UUB]

I think, will be great somethin like KISS TNC over UART. For BBS, Packet Radio, APRS. Is possible?

[kronicd]

Absolutely I would love to see this. With the new AFSK messaging support it seems it would be a matter of adding UART instead of keyboard/display IO and it would be incredible!

An AUD$28 HT with a KISS TNC onboard would be an absolute game changer.

Not that the spectrum graph and RSSI implementation isn't already a game changer... Thanks for the amazing work!

[kronicd]

After testing I have confirmed that BK4819 produces FSK, not AFSK. It will not be useful for general ham radio packet radio (APRS/BBS).

UART FSK may still have some use, but will not be compatible with existing ham infrastructure.

[troilus]

After testing I have confirmed that BK4819 produces FSK, not AFSK. It will not be useful for general ham radio packet radio (APRS/BBS).

UART FSK may still have some use, but will not be compatible with existing ham infrastructure.

Is FFSK work?

[drspastic]

from the datasheet:
Besides speech communication, the
BK4815N on-chip FSK data modem
supports F2D and F1W emission to be
used in both FRS and DPMR band for text
message and GPS information exchange.

[kronicd]

If the message functionality could be moved to use F2D then it should work with APRS & BBS :O

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[kronicd]

BK4819_Datasheet_V1.01.pdf

The BK4819 datasheet here states that F2D is indeed included!

[darksidelemm]

If it indeed does support AFSK (which i think the register map is calling FFSK1200/2400) there are some other considerations:

• APRS / packet uses NRZI encoding. This would have to be encoded/decoded in software.
• Apparently packet transmissions use a preamble of 0x7E. It looks possible to configure the FSK modem to use custom sync bytes, and only use 2 of them, so you could maybe set these both to 0x7E and have it trigger on an APRS packet?

Certainly some interesting possibilities, but lots of testing to be sure it works!

[rogerclarkmelbourne]

Generation of NRZI encoding is trivial, there is plenty of code to generate this on github

The flag bytes 0x7e have to be NRZ encoded before sending, so you just build the entire packet including the flags pramble and then send it to the chip.
You just don't include the flag bytes in the CRC calculation
Then assuming the baud rate can be set to 1200 and the tones set to 1200 and 2200Hz , it should work.

[darksidelemm]

Sure, encoding will probably be fine. Reception might be more difficult...