Enhanced Class 1 Bluetooth v2.1 Module
Hardware Integration Guide
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www.lairdtech.com/bluetooth
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CONN-HIG-BT740
Note: The serial module output is at 3.3 V CMOS logic levels. Level conversion must be added to
interface with an RS232 level compliant interface.
Some serial applications link CTS and RTS to remove the need for handshaking. Laird doesn’t recommend
linking CTS and RTS other than for testing and prototyping. If these pins link and the host sends data at the
point that the BT740 deasserts its RTS signal, there is significant risk that internal receive buffers will overflow
and cause an internal processor crash. This also leads to a connection drop and may require a power cycle to
reset. Laird recommends you follow the correct CTS/RTS handshaking protocol for proper operation.
5.2
SPI Bus
The module is a slave device that uses terminals SPI_MOSI, SPI_MISO, SPI_CLK, and SPI_CSB. This interface is
used for program firmware updates ONLY at the factory. Laird supplies a PC-based utility to allow a firmware
upgrade over the UART port. Laird highly recommends that customers use this method for updating
firmware.
Note: The designer should be aware that no security protection is built into the hardware or firmware
associated with this port, so the terminals should not permanently connect in a PC application.
5.3
PCM Interface
PCM is not supported in Firmware. PCM interface (PCM_OUT, PCM_IN, PCM_CLK, and PCM_SYNC) exists in
HW only.
5.4
General Purpose I/O and ADC
5.4.1
GPIO
Seven lines of programmable bi-directional input/outputs (I/O) are provided that can be accessed either via
the UART port or Over-the-Air (OTA) from a second Bluetooth unit. These can be used as data inputs or to
control external equipment. By using these in OTA mode, a BT740 module can be used for control and data
acquisition without the need for any additional host processor. Each of the GPIO[3:9] ports can be
independently configured to be either an input or output. A selection of ports can be accessed
synchronously.
The ports are powered from internal VCC_3V3. The mode of these lines can be configured and the lines are
accessed via S Registers (see the
).
5.4.2
ADC
The BT740 provides access to two 8-bit ADCs (Analogue 0 and 1). These provide an input range of 0 mV to
1,800 mV, which are read using the S registers (see the Firmware User manual).
Suitable external scaling and over-voltage protection should be incorporated in your design. The module
provides five samples per second at the UART with a baud rate of 115,200 or above.
5.5
BT740-SA On-board Chip Antenna Characteristics
The BT740-SA on-board chip monopole antenna radiated performance depends on the host PCB layout.
