This thread explains in detail the boot process for the 2073XS: firmware programming through FTDI VCOM 22 to BCM20736S
This part is important since there will be no valid configuration found within your empty EEPROM:
If no valid configuration was found, the next step depends on whether the HCI_UART RX pin is asserted or not:
• If HCI_UART RX is asserted, the part enters recovery mode
• If HCI_UART RX is NOT asserted, the ROM will assume all default configuration settings and then boot up into download mode
In addition, the selection of the correct external FTDI programming cable is critical as well.
Recovery mode is explained in the WICED Smart Quick Start Guide (SDK 2.x and TAG3 Board)
Our board has HCI UART Rx is pulled high, but it looks like the missing piece was the state of SDA when the chip comes out of reset (/RESET set high). Adding a button that holds SDA to the EEPROM high similar to the 20736 dev board we have allowed the programming to succeed.
Thanks for your help!,