Flash programmable means that you can program the Flash memory off the chip. Field programmable means that the Flash memory of the chip can be programmed at your end (on Field) without having to program the chip at the factory (Manufacturing site). Essentially, the Field programming can be considered as a means of programming the Flash programmable devices and there is no direct comparison between Field programming and Flash programming. Please note that only the volatile registers can be programmed using the I2C interface. The non-volatile registers are field programmed using our CY3672-USB Programmer or any other Cypress Certified Programmers like BP MicroSystems, Hi-Lo Programmers etc. For Field programming these non-volatile registers, you have to remove the chip from your board for programming. However, when you use Serial programming interface, you can program the volatile registers without removing the device chip, In-System using I2C interface which your board should provide with.