Texas Instruments CC2520, User Manual

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Figure 24 - SPI Mode 1
This mode allows uninterrupted use of the communication bus to the EM while using
peripherals on the EB (typically updating the LCD or accessing the serial flash) at the
expense of requiring two serial interfaces on the microcontroller.
8.3.2 SPI Mode 2 (SPI_M2)
An alternative mode is to use only one SPI bus for all devices. This is achieved by using SPI
mode 2.
Figure 25 - SPI Mode 2
In this case, USCIB0 is used for accessing both the SPI devices on the EB and the EM. In
some cases, this might complicate software, as it needs to make sure ongoing SPI
transactions are not interrupted prematurely (e.g. interrupt from radio triggers reading from
the transceiver using the SPI bus while the MCU is in the middle of writing to the LCD).