FT817 keypad - serial communication quirks

Wondering where the FT817 keypad has gone? Don't worry, I'm working on it every night. All the one-way features have been implemented and tested: direct frequency dial, mode change, VFO toggle and frequency presets. These controls only require to send data to the radio.

What was left instead requires to read two bytes from the radio, modify one or two bits and return them back.

While the software side has been implemented correctly, I didn't seem to be able to read bytes, thus writing back wrong settings to the FT817(ND). Many hours have been spent in visualizing on 8 LEDs (one byte) what was being received, processed and sent.

The most probable cause is to be found in the ATtiny2313 internal RC clock source. I did look for its beat at 8 MHz, but all I could hear was some wideband noise. Even at 4800 baud the tiny2313 is probably too off to read proper data.

I am completing a pre-production prototype with an external XTAL source. It will run at 14.7456 MHz, that gives a 0% error rate according to the uC datasheet. Theoretically it will be possible to increase the serial communication rate up to 38400 baud (FT817 maximum), but perhaps overall reliability would suffer.

If I manage to master these advanced controls, all sorts of customizations will be possible, from key-function remapping to new/different controls. A UK HAM has already asked me to have 60m presets on the keypad. The only limit is the chip program memory: 2kbytes.