I spent some time reading inHM-TRP Series 100mW Transceiver data sheet as well as SiK source code I wanted to know that if the 433MHz and 913 MHz is something fixed in the chip, that is why modules are sold either 433 or 913 or it is something you can change EASILY :)
Luckly I found that frequency is something not fixed, however in the source code of SiK, it is stored in board_frequency as input preset parameter when building the code, and it is passed to the firmware part in main.c where it is used for initialization.
Well I decided to make minor change, I added a new variable -the 16th variable- called Main_Freq
it can be given the following values
FREQ_433 = 0x43,
FREQ_470 = 0x47,
FREQ_868 = 0x86,
FREQ_915 = 0x91,
These values are defined in board_info.h file
Typical steps to change frequency are:
- +++ to enter AT commands mode.
- ATS16=67 to change to 433 MHz
- AT&W to save settings
- ATZ to reboot (Mandatory)
Another interesting thing is that the chip originally support frequencies as low as 240 MHz, however the firmware does support the above four frequencies only.
Now if you need to change frequency using only Firmware without the need to update the Bootloader you can use my changes...I hope you find this useful.
Please note that you should use proper antenna for each frequency