The Front panel and the Main unit of the popular Low power transceiver Xiegu G90 are connected through a DB9 cable.
The Main unit and the Front panel have, each other, separate firmware upgrade procedures meaning. This meaning the user has to acces the upgrading UART on each part of the radio.
Between the two parts, information is exchanged via UART also. The Main unit is sending information from the I/Q detector used to show the nice waterfall on the LCD and the Front panel is sending frequency and mode (and other various DSP settings) to the Main unit.
From practical observations, the protocol used between the Main unit and the Front panel is modified on the fly, with each "improved" version therefore, different versions of FW cannot be used (with one exception at this moment, DisplayUnit FW 1.76 and MainUnit FW 1.77. (download link).
Possible causes for this, as far as the time of this post;
1. Improper contact on the separation cable.
2. a- Incompatible FW versions (see the above note about FW1.77).
b- No FW in the Main unit. This will be detailed.
3. Physically broken UART either on Front panel or in Main unit.
Note about 2.b- The FW procedure means that you must connect the radio to the power supply with the serial programming cable (3.5mm stereo jack), start the PC software, power ON the radio and send "1" from a terminal window. What happen next is that the content of FLASH memory of the microcontroller is erased. So, no FW in the uC.
If the cable is left into the programming jack, at the power on, a stray "1" can be accidentally sent thus erasing the FW. The Front panel uC will wait for the right flag on UART and after a while it will signal that the serial communication is not possible. The solution is simple, you must reflash the Main unit (with the right version of FW, of course).
This apply also on 2.a.
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