RN42/RN41 - USB and SPI bus usage

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.

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