How to connect PIC18LF4550 to BTM411 Bluetooth module

Hello Everyone,

I'm working on a project where I'm using the PIC18LF4550 to send and receive information to the PC via bluetooth. I am using the BTM411 module on my circuit and I will be using the BT211 bluetooth Adaptor on the PC.

I need to know how to connect the pins of the BTM411 module to the PIC18LF4550, as in what pin should be connected to the PIC18LF4550 and what pin should be connected to other things etc.

Please note, I will be connecting BTM411 in my own circuit not in a development kit or anything, so please tell me if I need any additional components or devices.

Please don't hesistate to ask if you need me to provide any more details.

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I assume you have the data sheet for the BTM411:

The schematic on page 63 shows how the BTM411 is wired on the development board.  You can copy the the power and ground connections.  You have a choice of UART of SPI for the data interface.  The PIC can accommodate either one.

SPI is probably the better choice.  If the BTM411 is the only SPI device, you can tie the Chip Select HIGH and deal with the 3-wire interface.


The data sheet should tell you how to terminate unused pins.
adkryAuthor Commented:
Hello d-glitch, and thanks so much for your great feedback. A friend of mine had a look and told me that SPI is used for audio codec thing, i.e. UART is the only interface that can be used to interface with the bluetooth module.

I did read the manual thoroughly, but I'm using this module on my board so I believe there would be difference than from the case of the development board.
adkryAuthor Commented:
ok I connected it in that way

The connections I need between the BTM411 and the PIC18LF4550 are as follows:

UART_CTS - Tells the bluetooth module that the PIC is ready - connected to any input/output pin in the microcontroller.
UART_RXD - Bluetooth module data input - connected to microcontroller UART TX pin.
UART_RTS - Bluetooth module uses this to indicate if it's ready or not - connected to any input/output pin in the microcontroller.
UART_TXD - Bluetooth module data output - connected to microcontroller UART RX pin
VDD_USB - connected to VCC = 3.3V
VDD_IO - connected to VCC = 3.3V
VDD_IN -  connected to VCC = 3.3V
RESET - Used to reset the bluetooth module - connected to any input/output pin in the microcontroller.

any comments/suggestions on that ?

Does RTS indicate the status of the modem, and is the RTS/CTS logic active-high?

Which handshake mechanism has to be used: RTS/CTS or DTR/DSR?

How do I code the microcontroller (using C language) to send/receive data through the BTM411 ?
Go back to the BTM411 Manual and digest the AT commands section.

You have to find a C library that lets you configure the PIC UART as an output device, and then send the AT commands to configure the BTM4111.  

Presumably you will have to do this for both ends of your Bluetooth link.  Not sure how may commands are required to configure and link the two BT modules.  Once they are linked, you should be able to send character data through.

To start up, it might be easier to connect the BTM411's to a serial port and send commands by typing in a DOS window.  

Once you have the BT configured properly, you can save the configuration so it will power up properly next time.

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