User Manual

RN41/42 Evaluation Kit User’s Guide
DS50002325A-page 34  2014 Microchip Technology Inc.
3.2.4 HCI Mode
RN41/42 module offers the Host Controller Interface (HCI) mode in addition to the stan-
dard operational mode of its Bluetooth modules (standard mode refers to the on-board
stack running on the module). In HCI mode, the on-board stack is bypassed and the
module is put in a state that runs the Bluetooth baseband. The HCI provides a com-
mand reference interface to the baseband controller and the link manager, and pro-
vides access to the hardware status and control registers. This interface provides a
uniform method for accessing the Bluetooth baseband capabilities.
In this mode, The Bluetooth stack is no longer on-board the module. It is offloaded to
the interfacing host processor. The Bluetooth module is used as a radio, performing the
lower level MAC functionalities, while the application stack runs on the host processor.
Using the module in HCI mode enables designers to implement profiles that are not
natively supported on the Bluetooth module.
RN41 module offers HCI mode in two hardware interfaces:
• HCI over UART (RN41/42HCI-I/RM)
• HCI over USB (RN41/42U-I/RM)
3.2.4.1 HCI OVER UART
In this mode, UART is the hardware interface between the host processor and the
Bluetooth module. User must interface the flow control signals between the host pro-
cessor and the Bluetooth module for the HCI inteface to work. Failure to do so can
cause the host processor and the Bluetooth module to become out of sync and break
the Bluetooth link.
3.2.4.2 HCI OVER USB
In this mode, USB is the hardware interface between the host processor and the Blue-
tooth module. In this architecture, the Bluetooth module is the USB slave and the host
processor is the USB host. Using the USB interface offers the advantage of a faster
data link between the Bluetooth module and the host processor. With this architecture,
it is possible to achieve Bluetooth’s theoretical maximum throughput of 3 Mpbs.
3.2.5 Using the SPI Bus to Upgrade the Flash Memory
While not required, this bus is very useful for configuring the Bluetooth module’s
advanced parameters. The bus is required when upgrading the module’s firmware. In
typical application schematic a 6-pin header can be implemented to gain access to this
bus. A minimum-mode version might simply use the SPI signals (4 pins) and obtain
ground and VCC from elsewhere in the design.
3.2.6 Minimizing Radio Interference
When laying out the carrier board for the RN41 module, the areas under the antenna
and shielding connections must not have surface traces, ground planes, or exposed
vias. For optimal radio performance, the RN41 module’s antenna end must protude at
least 5 mm beyond any metal enclosure.
3.2.7 Low Power
For RN42, to achieve low-power operation, hold the module’s RESET pin low. With
RESET = 0 VDC, the module consumes 35 uA of power. If RESEST is left floating or
high, the module consumes 3 mA in Sleep mode. To obtain the lowest power, the RN42
must be passive (in Slave mode and not trying to make connections).
Note: HCI mode requires a separate firmware build that must be loaded into the
module’s flash at the factory. It is not upgradeable in the field.