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Peripheral Only: Bluetooth
as a transparent cable
replacement
Operation of the Bluetooth module with
command control serves functionality
– for example configuration in ongoing
operation – and is ideal in terms of
safety considerations (checksum).
But sometimes the requirements are
different.
Alongside operation of themodule using
commands, there is the "Peripheral
Only” mode in such cases. Upgrading
of devices is possible thanks to the
transparent UART interface, whereby
modification of the serial interface is
neither desired nor possible. These
could be industrial machines with an
existing RS232 interface for instance.
The manufacturer Amber wireless
intentionally introduced the option
of operating the wireless module
as ‘Peripheral’ in the sense of the
Bluetooth protocol, as this is interesting
for very many applications. Devices
are equipped with this kind of wireless
module so you can connect with them.
This means that pairing is initiated by a
mobile device. Even without command
control that would be necessary to
switch off the module that is not
required, AMB2621 is particularly
power-saving in the “Peripheral Only”
operating mode, as the UART interface
is only active on establishing a wireless
connection. Uncomplicated static
passkey pairing is used as a security
feature, as in the hands-free car kit.
AMB2621 with Peripheral mode is
recommended whenever the module
does not initiate any connections
itself (i.e. it is only contacted from
the outside) or no user interface can
be implemented, as the rest of the
product is already finished.
Bluetooth is the “cable replacement” in
this application and communication is
correspondingly simple. In the above
example, in the “Peripheral Only”
mode the host would only receive
“Hey AMB2621!” without header and
checksum bytes and would only need
to send “Hey App!” to the module such
followed by a 2-byte length field, the command-specific payload data and
the attached checksum, which guarantees correct transmission of the byte
sequence.
The following example shows how this syntax looks in practice.
In the case in which a smartphone with MAC 0x825CA7E287D0 connects with
AMB2621, the AMB2621 sends the following notification via UART (Universal
Asynchronous Receiver Transmitter) to the host connected:
0x02
0x86
0x07 0x00 0x00 0x82 0x5C 0xA7 0xE2 0x87 0xD0 0x4F
(connection to the device with MAC 0x825CA7E287D0 is opened)
0x02
0xC6
0x08 0x00 0x00 0x82 0x5C 0xA7 0xE2 0x87 0xD0 0x13 0x13
(connection to the device with MAC 0x825CA7E287D0 has been opened
If the smartphone now sends a notification “Hey AMB2621!”, e.g. with the help of
the AMB2621 toolbox app, the AMB2621 transmits the following data via UART to
the host connected:
0x02
0x84
0x13 0x00 0x82 0x5C 0xA7 0xE2 0x87 0xD0 0xC8 Hey AMB2621! 0x89
(Data have been received from the device with MAC 0x825CA7E287D0. The data
Start signal Command
Length
Payload
data
Checksum
byte 1
byte 1 bytes, least sig� 2
nificant byte first
x bytes
byte 1
The commands of the AMBER firmware stack follow a simple structure:
The commands of the AMBER firmware stack follow a simple structure:
Command
Description
0x04
Send data
0x84
Data have been received
0x86
Connection is established
0xC6
Connection is open, data transfer now possible
46 l New-Tech Magazine Europe