RN42APL datasheet(9/26 Pages) MICROCHIP

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 2015 Microchip Technology Inc.

DS50002328A-page 9

RN42/RN42N

FIGURE 2-5:

RN42 HOST PCB EXAMPLE LAYOUT

2.5

External Antenna Types (RN42N)

The RN42N module’s antenna pin (pin 26) provides a

50-ohm impedance to external antennas. Pin 25 can

connect directly to a coaxial cable or to an antenna

connector such as a U.FL or reverse polarity SMA.

The PCB trace from pin 26 to the coaxial cable or con-

nector should be less than 0.2 inches (5 mm) for mini-

mum loss and the best impedance match. If the PCB

trace is longer, it should be a 50-ohm impedance

microstrip trace. Connect adjacent ground pins 25 and

27 to a low-impedance ground on the host PCB and the

antenna connection. Figure 2-4 gives example host

PCB layout to a U.FL connector.

2.6

HCI Mode

Microchip offers the Host Controller Interface (HCI)

mode in addition to the standard 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 base-

band. The HCI provides a command reference inter-

face to the baseband controller and the link manager,

and provides 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 pro-

cessor. The Bluetooth module is used as a radio, per-

forming 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.

Microchip offers HCI mode in two hardware interfaces:

• HCI over UART (RN42HCI-I/RM)

• HCI over USB (RN42U-I/RM)

2.6.1

HCI OVER UART

In this mode, the hardware interface between the host

processor and the Bluetooth module is the UART con-

figured at 115.2Kbps. The UART hardware flow control

signals are required between the host processor and

the Bluetooth module for the HCI interface 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.

2.6.2

HCI OVER USB

In this mode, the hardware interface between the host

processor and the Bluetooth module is the USB. 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 interface, it is possible to

achieve Bluetooth’s theoretical maximum throughput of

3 Mpbs.

No Copper

in these

areas

RN42

Okay

RN42

Best

RN42

Okay

RN42

Okay

Note:

HCI mode is only available by ordering

part RN42HCI and RN42HCI for UART

interface; or RN42U and RN42U for USB

interface.

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