RT-880 Some Assumptions
Added 2025-07-02 11:01:17 +0000 UTCReverse Engineering Update: Early Insights and Theories
The reverse engineering journey is in full swing, and here are some early discoveries:
Pins 8 & 9 are clearly multiplexed. One function is the Si4732 data I²C line, but the other labels show both as CODE2-ADIN. I suspect a typo here, they’re likely CODE1 and CODE2, with ADIN hinting at ADC input pins.
Pin 25 (FM-POWER-EN) is probably the Si4732’s reset (RST) signal. When pulled low, the Si4732 resets, communication pins float (tri-state), freeing pins 8 & 9 for other uses. My theory? CODE1 and CODE2 detect GPS module presence. I plan to bake a test into the diagnostic firmware, but I’ll need the community’s help, especially comparisons between GPS and non-GPS units.
Pin 11 (ANC-POWER-EN) seems tied to active noise cancellation. Almost certainly essential for crossband repeater functions and possibly full duplex operation.
Pins 6, 14, 15, and 16 (labeled “868”) probably connect to the APRS modem.
Pin 21 (Tone) looks like an audio path injector, likely PWM configured as PCM to generate audio signals like voice prompts.
Pin 23 (LOW_BATT_DET) is probably misnamed; it’s likely the ADC input reading the battery voltage divider, monitoring battery level.
Pins 61 & 62 appear unused, leftover from the BK1080 chip, which the Si4732 replaced.
Pin 59 (EAR_DET) likely detects whether something is connected to the Motorola side port.
Comments
LMAO, I like that. But so long as I make enough to pay the bills and offset the work hours I lose elsewhere I'm happy, this was never about making a fortune, I just want to work, doing what I love for living, that way we all win.
Marcus Dudley
2025-07-03 14:40:51 +0000 UTCJust upgraded my membership in here specifically for the 880 work (and whatever comes next I'm sure). I have the 880G and I love it. Even though I'm a bit of a noob despite owning more than my share of HTs. The 880G is by far my favourite and I can't wait to see how much you improve its use! (PS: if you're looking for more income from this route, why not sell some merch? I think a lot of us in here are nerdy enough to wear it on our sleeves. something like "Nicsure, I void warranties with quality" or the like).
Douglas Morse
2025-07-03 13:15:26 +0000 UTC
