Over a year ago we updated the firmware / hardware for the CFA635 family. Part Change Notice #10280 on 2010-04-10 announced the change in firmware from 1.4 to 1.6. The primary change was moving from a hardware reset to a firmware reset. To disable the hardware reset, R8 is no longer loaded on the CFA635. To accommodate a wider voltage tolerances, the clock speed of the micro-controller was slowed down.
If your code follows the recommended guidelines of packet reconciliation - waiting to send the next packet after the module sends back an ACK - you should not have any issues communicating. If you are using timing for communicating with the CFA635, then this may explain why you are not able to communicate with the modules. Each one was tested and fully functional when it left our facilities.
As an additional note, we have announced the End of Life of the CFA635. It will be replaced by the CFA735:
You can also subscribe to receive the notices via email for any part that you use, or any PCN that we issue. For individual parts, you can subscribe on the Notices tab. If you wish to subscribe to all parts, you can subscribe via the PCN page: