Programmable integrated circuits work by first accepting a custom circuit design from a programmer and then processing that logic when installed in a circuit board. Some programmable chips can be erased and reprogrammed, while others are read-only.
Like all integrated circuits, a programmable chip contains many logic gates that are each designed to respond to electronic signals received by the chip's external pins and work together to execute a process. With a programmable chip, that process is not established when it is fabricated. The logic gates are created with material that acts either as a fuse, to break the connection to the gate, or as a connector, growing a link to the gate. The logical process is determined by changing this material. Before installing the chip in a circuit board, a programmer uses a device known as a burner to modify the chip, burning the fuses or growing the connections, in order to set the logical process within the chip.
Once installed on a circuit board, the chip functions in the same manner as any integrated circuit. It receives electronic signals through the external pins. Those signals flow through the logic gates according to the logical process the programmer established, eventually sending electronic signals back to the circuit board through the external pins.