Was there a Rabbit RMC3110 serial port change with Rev C?

With Rev C not receiving serial data on boot up when powered from PC. Was chip changed?

Can you provide some more details?

Rev C of what? The RCM3110? How do you have your hardware set up? Is it in a development board? How are you supplying power? Is this running code from Dynamic C, or a binary installed with RFU?