User's Manual

Enhanced Class 1 Bluetooth v2.1 Module
User’s Guide
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CONN-GUIDE-BT740_v0.2
5 AT COMMAND SET
5.1 Introduction to AT Commands
This chapter describes the ‘AT’ protocol used to control and configure the BT740-Sx Bluetooth modules
after it is configured to present an ‘AT’ protocol instead of the alternate multipoint packet-based interface.
The Multipoint Protocol is also described in this document.
The protocol is similar to the industry standard Hayes AT protocol used in telephony modems, as both
types of devices are connection oriented. The extended AT command set makes the Laird device
performs the three core actions of a Bluetooth device: establish Bluetooth connections, pair, and inquire.
Many other provided AT commands perform ancillary functions, such as trusted device database
management and S Register maintenance.
Just like telephony modems, the Laird device powers up in an unconnected state and only responds via
the serial interface. In this state the Laird device can respond to Bluetooth Inquiries. Then, just like
controlling a modem, the host issues AT commands which map to various Bluetooth activities. These AT
commands have appropriate counterparts in the alternate multipoint packet based protocol which also
achieve the same goal.
The nature of ‘AT’ protocol allows it to control and manage only one connection at a time; this is in
contrast to the multipoint packet protocol which can simultaneously control many connections. The main
advantage ‘AT’ protocol offers is simplicity.
The module has a serial interface through which the ‘AT’ protocol channels, which can be configured for
baud rates from 1200 up to 921600 and has an RF communications end point. The default baud rate for
AT command mode modules is 9600 bps.
The RF communications endpoint has a concept of connected and unconnected modes and the ‘AT’
protocol at the serial interface has a concept of command and data modes. This leads to the matrix of
states shown below.
RF Unconnected
RF Connected
Command Mode
Allowed
Allowed
Data Mode
Illegal
Allowed
The combination ‘Data + RF Unconnected Mode’ does not make sense and is ignored.
Navigation between these states uses the AT command/responses, described in detail in subsequent
sections.
There are many references to the term ‘S Register’ in the rest of this document. These are an array of
integer values stored in non-volatile memory which are used to configure the module so that it behaves in
a certain way after powering. These ‘S Registers’ have two attributes; a value and an ID. The ‘ID’ is a
positive integer number used in appropriate commands to read/write the values.
5.2 AT Protocol Mode
5.2.1 AT Protocol Assumptions
The CSR (Cambridge Silicon Radio) Bluetooth chipset in Laird devices has limited memory resources.
Therefore it is NOT proposed that there be full implementation of the AT protocol as seen in modems.