GHI FEZ CERBb40 NF
The board here used is a GHI Fez Cerb40 based upon an STM32F405RGT6 supporting a 1MB Flash and up to 192KB RAM in a LQFP64 package. On this board the LSE is soldered in case you have a board without the LSE please make sure you have it configured correctly in both the mcuconf.h files for nanoBooter as well as nanoCLR.
The available pins have been set as can be read in the board.h file and it is there where you can set the pin usage for your required use. Visiting the official site here and per datasheet looking at Table 9. Alternate function mapping you will find possible alternative uses of the various pins. In its initial release the following pin configuration and usage has been verified. Looking at the board from the above (MCU visible) and with the USB connector at the top we have pin 1 on the left hand side.
|11||PB9||I2C1 SDA||Confirmed and working||2018-02-07|
|16||PB8||I2C1 SCL||Confirmed and working||2018-02-07|
|18||PB7||UART1 RX||Confirmed and working||2018-02-09|
|19||PB6||UART1 TX||Confirmed and working||2018-02-09|
|20||PB5||GPIO, PWM||GPIO confirmed, PWM not done yet||2018-02-07|
|28||PA2||UART2 TX||Confirmed and working||2018-02-08|
|29||PA3||UART2 RX||Confirmed and working||2018-02-09|
|32||PB10||I2C2 SCL||Confirmed and working||2018-02-07|
|33||PB11||I2C2 SDA||Confirmed and working||2018-02-07|
For more information on the board specifics you can have a look at the GHI Electronics Cerb40 page
NOTE: this configuration was successfully tested in a GHI_FEZ_CERB40_NF board using the Serial over USB connection on USB port 1 that creates a virtual COM port.
Checkout the C# managed helpers available for this board.