This is my new BIG project. I am starting on a TNC-2 type clone TNC.
This TNC design utilizes a PIC16F84, MX-614 modem IC and a MAX-232. It's hard to say what is really the "heart" of this design. The PIC16F84 is basically the brains, it will control the overall actions of the TNC. The PIC also allows for a user interface to the terminal program and also controls the mode of the MX-64 chip.
The MX-614 really is what makes this design more simple than a standard off-the-shelf TNC. Instead of modulating and demodulating FSK in the PIC's firmware, the MX-614 will do this for us. This allows me more room to write the control firmware for the TNC in the PIC and leave the actual data work to a seperate IC.
The MAX-232 lets the PIC have a easy to use interface to the computer's serial port. The MAX-232 will take the UART TTL signals and convert them to RS-232 levels for the computer to understand, like-wise it will take the RS-232 from the computer and convert it back to TTL for the PIC to understand.
This is a beginning schematic of the TNC. I sure it will undergo some changes and tweaks as the project unfolds. (1/16/02)