The bootloader communicates with an external device over a 2-pin universal asynchronous receiver and transmitter (UART) or a 4-pin SPI. The SPI port has the advantage of supporting higher and more flexible data rates, but the port also requires more connections to the CC23xx and CC27xx devices. UART has the disadvantage of having slightly lower and possibly less flexible rates. However, the UART requires fewer pins and can be easily implemented with any standard UART connection.

There are three possible configurations for the serial interfaces for CC23xx devices and only one possible configuration for the serial interfaces for CC27xx devices. Table 3-2 and Table 3-3 specify which serial interface signals are configured to specific DIOs for CC23xx and CC27xx devices, respectively. Configuration of the ROM Bootloader is done between the FCFG and the CCFG. There are defaults that are set in the FCFG that take effect if a valid CCFG is not present on start-up. The default configuration is dependent on the device package. Please see the device-specific technical reference manual for which configuration is the default configuration for a given packaging. If users want to alter the defaults set by the FCFG, then update the CCFG to provide the behavior desired.

The bootloader can be configured to trigger unconditionally or can be configured to trigger with a pin. Pin trigger can be enabled in Sysconfig by going to the TI DEVICES section under Device Configuration in Boot Configuration and by setting the Enable Pin Trigger option. The Pin Trigger DIO can also be set at the same place in Sysconfig. The default Pin Trigger DIO for ROM bootloader can be found in Table 3-4.