Digilent PmodBT User Manual

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Revision: January 17, 2011
Note: This document applies to REV C of the board.

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Overview

The PmodBT is a wireless communication
peripheral module with a fully-integrated
Bluetooth interface. The PmodBT’s simple
UART interface and profile support let you use
the module’s robust functionality with a
minimum of extra code. This makes it the
perfect solution for embedded wireless
communication between a PC, PDA, or smart
phone and any number of remote applications.

Features include:

• a National Semiconductor LMX9838
Bluetooth serial port module

• a UART interface

• a 12-pin header Pmod interface

connector

• a wide range of profiles including the
Generic Access Profile, Service
Discovery Application Profile, and the
Serial Port Profile

• 2.5V – 3.6V operating voltage

• a small form factor: 0.8” x 1.5”

Functional Description

The PmodBT provides Bluetooth support in
either a transparent cable-replacement mode
or a more powerful command mode. The main
communication interface with the PmodBT is
the UART on J1 with hardware handshaking
and a hardware reset pin.

UART Interface

The UART interface’s factory default setting
uses eight data bits, no parity bit, and one stop
bit. The baud rate is selectable via the mode
jumpers of J2. Table 1 gives some sample
baud rate settings for J2. A ‘1’ signifies a
shorted jumper and ‘0’ signifies open.

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National

Semiconductor

LMX9838

J2 Pin 5
(OP5)

VCC

1 2

4

3

65

J2

Baud

OP3
OP4

OP5

RTS

1

RXD

2

TXD

3

CTS

4

GND

5

VCC

6

NC

7

RST

8

NC

9

NC

10

GND

11

VCC

12

J1

J2 Pin 1
(OP3)

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PmodBT Block Diagram

J2 Pin 3
(OP4)

1 0 0 Select from

NVS Table
1 0 1 9600 bps
1 1 0 115.2 kbps
1 1 1 921.6 kbps

Table 1 UART Speed Select Jumper Settings

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PmodBT Reference Manual

The factory default for the “Select from NVS
Table” setting (1,0,0) is 9600 bps. Changes to
the factory default communications settings are
in effect until you issue the “Restore Factory
Settings” command.

The UART interface relies on the two hardware
handshaking signals RTS and CTS to
determine when data can be sent or received.
These signals are used by both the host and
the PmodBT to indicate a low buffer situation.
The PmodBT takes input from the host
controller on CTS and supplies output of buffer
conditions on RTS. If hardware handshaking is
not being used by the host application, CTS
must be pulled low or the PmodBT will not
send data.

Table 2 describes the signals assigned on
each pin of the PmodBT 12-pin header.

Command Mode

The LMX9838 Bluetooth serial port module on
the PmodBT uses a command protocol for all
commands sent or received through the UART.
These commands are the basis for
communicating with the module by the host
device.

Transparent Mode

The Bluetooth module has a transparent mode
in which the module acts as a pass-through for
serial communication between the host and a
single Bluetooth device.

The only way to exit transparent mode is to
use a UART_BREAK signal, defined by
holding the receive line low for longer than
164µS, or the hardware reset.

For more information on the command and
transparent modes, see the LMX9838
Software User’s Guide at the National
Semiconductor web site.

Connector J1 – UART Communications
Pin Signal Description

1 RTS Ready to Send
2 RXD Receive
3 TX Transmit
4 CTS Clear To Send
5 GND Power Supply Ground
6 VCC Power Supply (3.3V)
7 NC Not Connected
8 RST Reset
9 NC Not Connected
10 NC Not Connected
11 GND Power Supply Ground
12 VCC Power Supply (3.3V)

Table 2 Interface Connector Signals

Power Supply

The PmodBT is designed to work with Digilent
programmable logic and embedded control
system boards that have 12-pin header
connectors.

The PmodBT requires a 2.5V-3V supply
voltage. A 3.3V power supply voltage is
available on all Digilent system boards and is
provided as part of the 12-wire Pmod interface
standard.

Digilent system boards with Pmod interface
connectors allow jumper selection of the power
supply voltage being provided to the Pmod.
Ensure that the system board is jumpered to
provide 3.3V to the module before applying
power to the board.

For more information on board specifications
regarding hardware tolerances and chip
architecture, see the LMX9838 Data Sheet at
the National Semiconductor web site.

www.digilentinc.com page 2 of 2

Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.