The intelligence of the E07-M1101D is accessed via a standard 4-wire SPI (Serial Peripheral Interface) bus. This occupies four critical pins: SI (Master Out Slave In / MOSI), SO (Master In Slave Out / MISO), SCLK (Serial Clock), and CSN (Chip Select Not). Unlike simpler RF modules (like the 433MHz ask/ook modules), the CC1101 inside the E07-M1101D contains dozens of internal configuration registers. The SPI interface is the gateway to these registers, allowing the engineer to program frequency deviation, data rate, output power, and channel filtering.