User's Manual

Enhanced Class 1 Bluetooth v2.1 Module
User’s Guide
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www.lairdtech.com/wireless
149
CONN-GUIDE-BT740_v0.2
13.8.5 UART Protocol Selection & Indication Via GPIO
S register 255 selects either MP(1) or AT(2) protocol mode for communications over the UART.
If S Register 255 is set to zero, then it implies that a GPIO selects the protocol such that zero sets AT
mode and one for MP mode.
To configure a particular GPIO pin for this functionality, set the appropriate S Reg (in range 50 to 65) to a
value of 14. Only the first S Register in the range 50 to 65 is used, any further S Registers with the value
14 are ignored.
In addition, if at least one S register in the range 50 to 65 is set to a value of 15, then on power up that pin
configures as an output and sets to zero if AT protocol is active and one if MP is active.
If S Register 255 is zero and no GPIO is configured for this functionality, then the protocol defaults to MP.
13.8.6 Firmware Upgrade via UART
The module has the capability of upgrading the firmware via the UART port using a Windows PC based
utility supplied by Laird.
Firmware upgrades over the air are not planned as this is not inherently supported by the chipset vendor.
The upgrade process requires a direct connection to RX, TX, CTS, and RTS lines of the module via
appropriate RS232 level conversion, to a built-in serial port on the Windows PC.
The new firmware deploys in a .dfu file as and when new firmware is available.
If the user requires the ability to upgrade the firmware when their product is in the field, then provision
must be made so that the RX, TX, CTS, and RTS lines are exposed to the ‘outside’ world. This is
complicated if, as in most usage cases, a host microcontroller drives the BT module in the user’s end
product. In that case, the host microcontroller drive the module’s RX and CTS input lines and hence
cannot also be driven by a Windows PC unless those two lines are gated appropriately.
One solution is incorporating the hardware logic illustrated below and use a USB to Serial adapter as per
http://www.ftdichip.com/Products/Cables/USBTTLSerial.htm which does not require RS232 levels.
Note: This solution should work in theory and Laird does not warrant that it will work given it has not
been implemented and tested. The purpose of the suggestion is to make the user evaluate the
convenience arising from it and variations thereof.