Laird BTM410 User Manual - page 34
34
www.lairdtech.com
Laird Technologies
BTM410/411
Bluetooth
®
AT Data Module
FACTORY DEFAULT MODE
Laird Technologies devices are capable of operating at a very wide range of baud rates. S Registers 520 and 521
allow the baud rate to be set very easily. The baud rate clock generator in the device is more versatile than
that available in a standard 16550 UART commonly available in PCs.
In fact, as long as the equation BAUDRATE * 0.004096 produces an integer value, then there will be 0%
error in clocking for that baud rate.
So it is possible to set a baud rate that a PC cannot cope with, and in that circumstance it is virtually impossible
to communicate with it.
To cater for this circumstance, if DSR is de-asserted, the device will come out of reset using 9600,N,8,1 comms
settings for exactly 750 milliseconds and then revert to the comms parameters as per the S Registers.
If the host sends the string !
then the module will remain at 9600,N,8,1 and will also configure itself using factory default S Register values.
MISCELLANEOUS FEATURES
This chapter describes various features which cannot be categorized appropriately.
RI dependent Start-up Mode
The UART_RI line can be configured as an input and on power its state can be used to force the device into
one of two modes. See description for S Registers 565 to 569 inclusive for more details.
For example, the feature could allow a device to make an outgoing connection if RI is in one state, and be
ready for an incoming connection in the other.
Pulse a GPIO pin
To flash a GPIO pin, set it as an output using S reg 610 and then use S reg 585 to 587 inclusive to set the pin,
period and duty cycle respectively.
Flash GPIO4 on Connectable Mode
S reg 534 now takes a value up to 2. A value of 2 configures GPIO4 so that it will blink when the module is
in connectable mode.
Reset via BREAK
The module can be reset by sending a BREAK signal. A BREAK signal exists when the module’s UART_RX input
is in a non-idle state (0v) for more that 125 milliseconds.
Digital I/O Cable Replacement
The module has a number of general purpose digital i/o pins. The direction of these are specified via S Reg 610.
When S Reg 531 is set to 4 at both ends of the connection, then on connection, any changes in the states of
the inputs at one end will be transmitted to the peer, which will then reflect those states on the appropriate i/o
pins if they have been configured as outputs.
It is recommended that the value of S Reg 610 at one end be the one’s complement of the other end. That
way, inputs at one end are mirrored at the other end and vice versa.
In addition S Reg 506 MUST be set to 0, which disables echos.
Note that due to inherent latency of Bluetooth transmission, expect the change of state to be delayed. This
value is typically 100ms and can be much more if the quality of the link is bad which results in many retries.
It is assumed that an audio channel is not active at any time.
Append Bluetooth Address to Friendly name
If S Reg 593 is set to 1, then the last 6 hex digits of the Bluetooth address are automatically appended to
the friendly name. This allows multiple devices with the same name in a neighbourhood to be differentiated.
CONFIgURINg
THE BTM410/411