Can I upgrade the firmware on the BT900 and/or BL600 without Flow Control (RTS/CTS)?

The firmware upgrade process requires Flow Control (RTS/CTS). The reason is because our BT modules need to see 0V on CTS (input) otherwise they won?t respond as CTS input is used to indicate if the other end is ready to receive data. However, you could tie CTS to GND and therefore hold it at 0V permanently rather than have it controlled by the host. That being said, we do not recommend that as this essentially turns flow control off and could cause data loss or worse, even the module to crash. It could work for low-throughput applications, but as mentioned above, it could cause problems.