how can I delete the RAM of the FX3 without turn-off power, to reprogram the FX3?
You don't need to erase the SRAM. Either reset the device or provide a second-stage bootloader which you can jump to in your firmware.
1. Reset Device: You can reset the device by calling CyU3PDeviceReset(CyFalse) to reset the device. It then enters the default bootloader which then boots the firmware according to what PMODE[2:0] is set to. See the FX3 datasheet's PMODE section for more details
2. Second stage bootloader: You can have a small bootloader always sitting in RAM which can bootload code for you. We supply a simple such bootloader which you can get from [SDK Root]\firmware\boot_fw. This bootloader loads itself into the top 32KB of the SRAM and you can jump into this from your firmware whenever you want to load new code.
See http://www.cypress.com/?id=4&rID=91261 and http://www.cypress.com/?app=forum&id=167&rID=72693 for more.
ok, thank you very much!