Why does the NRF51422 S210 device reset itself if I send more than 9 bytes to the UART from a PC?

Question

If I have the PC insert 1msec byte spacing between data bytes sent to the NRF51422, it receives the message and doesn't reset. I can send messages less than 10 bytes to the NRF51422 all day long without any issues without the need of any byte spacing. I have verified that my UART receive buffer is not overflowing (circular buffer). I have the baud rate set to 115200. I have tried other baud rate values with the same luck. I am using flow control on the NRF51422 (RTS/CTS) and PC. I really don't want to place inter-byte spacing on the data being sent from the PC. I'm not big on "band-aids". ;) 
 FYI: I'm sending serial data from the PC via an FTDI usb to serial cable (3.3V version).

michaelbester101 · Accepted Answer

Well, it ended up being the FTDI USB to Serial Cable (3.3V version). I'm not sure why, but if I reprogram the FTDI eeprom with a new descriptor and VID/PID, the 3.3V VCC power line sags whenever a serial transmission is being sent from the PC. The VCC line decays at a steady rate while TX is happing. It just happens that it takes 10 bytes sent at 115200 baudrate of time for the voltage to go below the minimum VCC operating voltage of the NRF51. When I added 1ms delay between bytes, the VCC line was able to go back to 3.3V prior to the next TX byte. I took an unaltered FTDI cable, read out the eeprom and program it's contents into my modified cables to get them back to "factory state". VCC is now stiff, with no droop during TX. I need to look closer at what happened. I'm curious to know what exactly caused this problem. :)