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Bluetooth and UART: A Complimentary Coupling
By Sylvie Kadivar, Marketing Manager, Datacom Products, Philips Semiconductors
Dong Nguyen, Applications Engineer, Datacom Products, Philips Semiconductors
Bluetooth is a popular standard for wireless communications. Integration of the technology is
rapidly expanding in the industry, as it is convenient, easy-to-use, and has the bandwidth to
meet the rapidly expanding demands of today's mobile and personal communication
applications. According to an In-Stat/MDR report published in April 2004, Bluetooth-enabled
applications of the future are expected to include cellular phones, cordless phones, access
points, desktop PCs, notebook PCs, memory cards, printers, digital camcorders and cameras, a
broad variety of consumer equipment (including games, speakers, set-top boxes and MP3
players), and automotive and industrial applications.
Bluetooth supports wireless point-to-point connections and wireless access to LANs, mobile
phone networks, the Ethernet and home networking devices. Bluetooth transmits and receives
data wirelessly through these devices. It delivers and receives the data transmitted through a
host system and a host controller interface (HCI).
Currently, the most popular HCIs are Universal Asynchronous Receiver and Transmitter
(UART) and Universal Serial Bus (USB) links, as illustrated in Figure 1. UART is often
preferred, as its performance and data throughput levels are nearly comparable to the USB
interface, while its simpler transport protocol enables decreased software overhead and a more
cost-effective overall hardware solution.
It is expected that a large percentage of Bluetooth chips designed for communication
applications will include a UART in the host controller. This article will examine the benefits
of using UART as a device to bridge the interface between the host and the Bluetooth
An Overview of UART
UART is typically used for communication with serial input and serial output devices. This
type of transmission reduces the cost and complexity of the wirings at the expense of speed. For
many applications, this tradeoff is ideal.
UART provides serial asynchronous receive data synchronization and parallel-to-serial and
serial-to-parallel data conversion for both the transmitter and receiver sections. These functions
are necessary for converting the serial data stream into parallel data, which is required by
digital systems. Synchronization for the serial data stream is accomplished by adding start and
stop bits to the transmit data to form a data character. Data integrity is insured by attaching a
parity bit to the data character. The parity bit is checked by the receiver for any transmission
To a host system, the UART appears as an 8-bit input and output port that it can read from and
write to. Whenever the host has data to be sent, it just sends it to the UART in byte format
(8-bits-wide). And whenever the UART receives data from another serial device, it will buffer
the data in its FIFO (again, 8-bits-wide), then it will indicate the availability of this data to the
host through an internal register bit or a hardware interrupt signal.
In addition to the transmitter and the receiver, some UARTs incorporate additional features
to significantly reduce software overhead and increase system efficiency. These features
o Hardware and software auto flow control to prevent FIFO overflow conditions
automatically. Without automatic flow control, the host software needs to empty the
receive FIFO immediately when it is about to be filled up.
o Large FIFOs to reduce the host processor's service time to the UART. This allows the
processor more time to do other tasks.
o Faster baud rate and faster bus access to improve the overall system performance.
The system can send/receive more data in less time.
UART to Bluetooth Interface: Off-the-shelf Bluetooth Module
One situation in which a UART interface can be beneficial is when it is working with an
off-the-shelf Bluetooth module. To illustrate this hardware interface, we'll examine a
real-world example revolving around the Free2Move Bluetooth Serial Port Plug (F2M01).
Many other products are currently on the market that are similar to the Free2Move plug and,
when integrated with UART, similar results should be produced.
The F2M01 integrates a Bluetooth module in very dense packing, which enables the
replacement of the most commonly used serial port cable. A class 1 Bluetooth is used, offering
a range of approximately 100 meters. No external drivers are needed to use the plug. A
user-friendly Windows application is included to program the communication modes as well as
the baud rate. The Windows application also enables hardware flow control using RTS/CTS
signals. Figure 2 illustrates the interface between the F2M01 and an existing serial port 9-pin
The F2M01 needs to be powered by an external power source of 4-5V DC through a DC
connector or a pin 9 of the RS-232 DSUB connector. The module can be connected to any
RS-232 serial port interface such as a PC serial port, or to any RS-232 9-pin DSUB connector.
The module offers data rates up to 115.2 Kbit/s.
UART to Bluetooth Interface: Bluetooth Chipset
Using UART as a bridge between a host and a device employing a Bluetooth chipset is another
situation in which UART proves beneficial. Again, we will use a real-world example to
illustrate the interface: the Philips PCF87752. The application of UART with Bluetooth
solutions from other manufacturers should run similarly and produce comparable results.
The PCF87752 is the most highly-integrated single-chip baseband solution designed for
Bluetooth applications. Known as "Blueberry DATA," it contains all the necessary elements to
provide applications with complete baseband functionality for Bluetooth wireless technology.
It is ideal for Bluetooth integration in hosted and some embedded applications like mobile
phones and computing devices.
The central processor in Blueberry DATA is an embedded 32-bit ARM7DMI RISC
microcontroller, offering very low power consumption per MHz. Several industry-standard I/O
interfaces are included in the IC in addition to UART. These include USB, I2C and PCM/IOM.
Because of the multiple I/O interfaces available, Blueberry DATA can communicate with a
wide range of devices. However, the simple transport protocol of UART results in less software
overhead and a more cost-effective hardware solution. Figure 3 illustrates such an interface,
while Figure 4 shows a detailed interface between a UART and host controller.
It is clear that Bluetooth will be a popular technology deployed for an array of applications in
the future because of its performance, convenience and ease-of-deployment. When integrated
with UART, the benefits are often amplified. Integrating a Bluetooth module onto a host
system through a glueless UART connection can provide designers with an optimal solution to
meet the growing demand for faster data rates and flexibility for today and tomorrow's