AN-1700| Application Note

LMX9838 Cable Replacement

National Semiconductor Application Note 1700 Sebastien Mathieu September 2007

1.0 Introduction
Bluetooth technology offers a wide range of features and profiles in order to support many different applications. Even though Bluetooth is very flexible, it still keeps the advantage of having a standardized wireless transmission. The growing success and wide distribution of Bluetooth in many different devices and applications make of Bluetooth an attractive solution to be used as general data interface such as simple cable replacement applications. National Semiconductor SimplyBlue module products include the complete Bluetooth stack and profile together with a great selection of features to provide an easy-to-use solution with minimal integration effort. This application note describes the main features and configurations required to implement the LMX9838 as cable replacement into a system.

2.0 Cable Replacement as "Waiting Device"
Implementing a cable replacement solution with a LMX9838 device only requires minimal efforts in software and hardware. The following details the hardware implementation, software implementation and a specific part on how to configure the device for production lines, in this specific scenario. 2.1 HARDWARE IMPLEMENTATION To connect a LMX9838 device in a system for a serial cable replacement application, the user should pay attention to the following points: All UART lines (TX, RX, RTS, CTS) should be connected to the host device. Omitting the flow control can bring up some corruption issues if the module works in transparent mode. In transparent mode the module forwards the data without interpreting and has therefore no way to control the flow. For more details on transparent mode refer to the "Software User's Guide". 1K pull ups should be applied to the OP pins which should be at high level. Table 1 gives the possible OP pins configuration and their respective UART settings... TABLE 1. General Baudrate
OP3 1 1 1 1 OP4 0 0 1 1 OP5 0 1 0 1 UART Speed Selection UART speed read from NVS UART speed 9600 bps UART speed 115200 bps UART speed 921600 bps

For more details and other configurations refer to the "Datasheet". The module should be powered according to the "Datasheet" values. The "Datasheet" also gives system schematics example to give some guidance. PG6 pin can be connected to one of the host IO as event trigger for the application. The PG6 pin goes high when a Bluetooth link is established on the module. Figure 1 shows a connection diagram example of a typical serial replacement application.

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FIGURE 1. System Diagram Example For Cable Replacement Application
Note: The UART selection in this example is set up to 115200 bps. PG7 acts as RF traffic indicator.

For more information refer to "Datasheet" and "Design Guide"

Bluetooth is a registered trademark of Bluetooth SIG, Inc. and is used under license by National Semiconductor Corporation.

2007 National Semiconductor Corporation

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