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DSH_BT024-00200_1v4 © Ezurio Ltd 2006
16
9.3
Pure Cable Replacement Mode
The module has the capability of being preset into a pure 5-wire data cable replacement mode. The 5 wires being
RX, TX, CTS, RTS and GND. This mode requires no changes to a host application since the
Bluetooth
connection is
automatically set up on power up. If the connection is lost the Embedded Intelligent
Bluetooth
Module will
constantly retry until the connection is reinstated.
By implication, two devices are needed to replace a cable. One device is pre-configured to always be a master
and the other, a slave.
Assuming the
Bluetooth
address of the master to be <bdaddr_m> and that of the slave to be <bdaddr_s>, the
master module is configured by sending it the following AT commands:
AT&F*
ATS512=1
ATS504=1
ATS507=2
ATS530=2000
AT&W
AT+BTR<bdaddr_s>
The ATS507=2 setting puts the device in DSR drop mode only. This means that when the device needs to be
reconfigured, deasserting the DSR line will ensure that the module responds quickly to AT commands. This further
means that in stand alone mode, the DSR input line MUST be asserted e.g. 0V in TTL signal mode.
The slave is configured by:
AT&F*
ATS512=4
ATS0=-1
AT&W
AT+BTM<bdaddr_m>
Where AT+BTM<bdaddr_m> is optional. If it is not specified, then the slave unit will accept connections from any
device. If specified then only connections from the device specified will be accepted.
If it is desired that the slave unit should not be discoverable (the master is by default not discoverable), then the
configuration commands are:
AT&F*
ATS512=3
ATS0=-1
AT&W
AT+BTM<bdaddr_m>
Where AT+BTM<bdaddr_m> is optional. If it is not specified, then the slave unit will accept connections from any
device. If specified then only connections from the device specified will be accepted.
When the units are next power cycled, the slave unit will wait for the master to connect to it and the master will
continually look for the slave. If a connection attempt fails, the master will wait for 2 seconds before reattempting
a connection. This 2 second delay can be varied by issuing it an ATS530 command with an appropriate value in
the range 100ms to 15000ms.
IMPORTANT NOTE: The DSR input to the module MUST be asserted for the auto connection to succeed. When
operating at TTL levels a 0V is seen as an assert state. When operating at RS232 levels and voltage greater than
3V is seen as assert. It is usual to connect the DTR line of the host to the DSR line of this device.