What is the use of the SPI bus for the module and should it be connected for firmware updates? Is the SPI bus activated with SPI_CSB low or high?
The Serial Peripheral Interface (SPI) bus is primarily used for factory programming, test, and diagnostics. Although not required, the SPI interface is useful for restoring a corrupted flash image or enabling test modes required for certification testing. When the module is installed in a final product that requires European type approval, we recommend that the SPI should be accessible via 6-pin header as shown in Figure 2.6 of the "Class 2 Bluetooth® Module with EDR Support" datasheet, available on the RN42 product page.
The programming firmware via SPI Interface refers to certification firmware. There are two methods available for special RN42 testing.
- Method 1: UART connection to RN42HCI module
- Method 2: USB/SPI connection to any RN42 SPI factory interface
Both methods require the BlueTest3 utility which is included in CSR's BlueSuite™ 2.5 software. Method 1 requires an RN41/RN42HCI module and access to the module's UART interface. Method 2 requires a CSR USB SPI programmer and access to the RN41/RN42 SPI interface. HCI modules are not needed for Method 2.