If you connect an XBee S3B module into a third-party interface board (such as the Sparkfun USB Explorer, or Parallax USB Adapter) you will be unable to communicate to the module using X-CTU. If you view the UART of the radio, you will notice a sequential series of numbers being generated. This is because several third-party interface boards have an LED connected to pin 6 of the XBee header. This LED provides an indicator for the RSSI (signal strength) for most XBees.
The XSC (S3B) and XSC (S3) modules have a slightly different pinout than the rest of the XBee product line. Pin 6 is used as a config line rather than an RSSI indicator. A legacy feature on the S3B is a diagnostic tool called "pitch mode", when the config line is pulled low during startup, it starts sequentially counting numbers and outputs it to the UART. This feature was originally used to perform a range test allows further backwards compatibility with the XStream radio.
Because an LED indicator is connected to this config line, the S3B module will enter pitch mode due to the pin being pulled low. There is no way to bypass this mode on the XBee itself. The best solution is to remove the current limiting resistor or LED on the interface board that is tied to pin 6, which will leave the pin unused. Please refer to the manufacturer's schematic of the interface board to locate these components.
