As was mentioned previously, the MCU connected to the Si1120 is responsible for setting the operating mode of the device by generating three control bits. Setting the mode is controlled by the SC, MD and STX pins and is a two step process since the MD pin is used twice. The SC pin is the shutdown pin and when high (logic 1) puts the Si1120 in a low power mode. To set the operating mode, the MCU starts by putting the Si1120 into the low power mode. Next, the MCU has to set the value of the first two configuration bits by setting the value using the MD and STX inputs. Once these bits are set, the SC pin is driven low latching the first two control bits (MD latch and STX latch in the figure) and bringing the Si1120 out of the low power mode. To complete the configuration, the MCU then drives the MD pin to either a logic 1 or 0 depending on the desired configuration (MD static in the figure). The MCU then holds this pin static for the time the Si1120 is to remain in the set mode. Since the MD static value is not latched, it can be used to change the mode of the Si1120 dynamically. For example, in the figure it can be seen that some values for the PRX50 mode, which uses MD (static), are set as a logic zero. The MCU can change the value of the GPIO used for MD and make it high at any time. This changes the Si1120 mode to PRX50H without having to go into the low power mode first.