XBee/XBee Pro Wireless Communicate with Microcontroller

Published by: pheysia on July 30, 2011.

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1.0 Introduction

The XBee and XBee Pro radio is made by Digi (formerly Maxstream) which is shipped with

firmware implementing the IEEE 802.15.4 protocol. These modules use the IEEE 802.15.4

networking protocol for fast point-to-multipoint or peer-to-peer networking. However, the most

different part between XBee and XBee Pro is they have different cover distance range for

communicate with own module. XBee can be covers around 30m at indoor and 100m at outdoor.

Inversely, XBee Pro can cover higher distance range than XBee which is 100m at indoor and

1500m at outdoor. Both devices that has a UART interface can connect directly from

microcontroller to pins of RF Module (XBee/XBee Pro). Using UART interface, we can use this

wireless devices to communicate between microcontroller to microcontroller (two PICs) or

between PC to microcontroller. Here, we will discuss how to use two XBee/XBee Pros to

interface with microcontroller and how to send command for configuration XBee/XBee Pro

Module.

2.0 Xbee/XBeePro hardware interface with microcontroller

Bear in mind, XBee is designed for 3.3V system, those use system will require extra work and

component before XBee module could be embedded in the system. So that, we used SKXBEE

(XBee Pro Starter Kit) as our example in this article. SKXBee can be used to interface for 5V

microcontroller board (SK40C+PIC16F877A). Any microcontroller with UART peripheral can be

used to interface with SKXBee. In this case, we have to connected XB_RX pin to PIC

Transmitter pin TxD (RC6) and XB_TX pin to PIC Receiver pin RxD (RC7). However, the

RESET button of SKXBee is optional case depend of user who would like the microcontroller to

reset SKXBee during run time. For more detail, you can refer to SKXBee User Manual on

Cytron website page (www.cytron.com.my).

The below figure has been shown as example hardware connection of SKXBee with

SK40C+16F877A:

The configuration of UART is complete, SKXBee is ready for embedded wireless

development. Trasmitting and receiving data require software or firmware development

on particular microcontroller. Before develop software programming, we should know

how to setting XBee Module Source address and Destination address, it is very

important for us to transfer data by transparently from one XBee module (Source) to

another XBee module (Destination).Two ways to setting ID address which is using X-

CTU software or using programming code to send specified command for XBee ID address

setting. We will discuss both ways in this article. In fact, user only need select one of

both ways to do it.

3.0 Using X-CTU software to setting Source address or Destination address.

X-CTU which is a computer based software to communicate with Xbee, to change configuration

or Transmit/Receive data. Double click the setup_x-ctu.exe file to install this software.

NOTE: Using X-CTU for address setting, SKXBee is no necessary

connect to microcontroller before the setting process is done.

Launch the X-CTU Software and connect the USB cable from SKXBee to computer USB port

(without connect to microcontroller). Select PC Setting tab> select serial COM Port >click

TEST/QUERY:

The box will show as figure below, click OK for close this box:

Basically, Xbee/XBee Pro has two command mode options which is AT Command Mode

and API Command Mode. Here, we only use AT Command Mode. The figure below AT

Command table is provided some commonly used for setting address:

All parameter are in Hexadecimal

format. For more detail of Xbee/XBee Pro command, please refer to User Manual of XBee/XBee-Pro

OEM RF Module.To send AT command and parameter, use syntax shown below:

NOTE: The failure to enter AT Command Mode is most commonly due to baud rate un-

match. Ensure the Baud setting on the PC Settings tab matches the interface data rate of the Xbee Module. By default, the baud rate should be 9600bps.

The below example shown how to check the previous Destination ID address of Xbee

module and how to change a new Destination ID address using WRITE command. To store the new value to non-volite (long term) memory, ATWR or atwr should be used

in AT Command Mode.

For modified parameter values to persist in the modules registry after a reset, changes must be saved to non-volatile memory using the WR (Write) command. Otherwise, parameters will be restored to previously saved values after reset. When a command is

send to a module, the module will parse and execute the command.

Upon successful execution of a command, the module return an OK message. If execution of a command results in an error, module will return ERROR message. For setting two SKXbee Source address and Destination address for communicate each

other, the command sending should same (parameter 1111 and 2222 can be change)

as below figure:

Now, we can write the coding to send command for setting SKXBee Source address and

Destination address. However, we have to refer the AT Command Mode table. The main reason

is the command code exactly same with the code we have using X-CTU software for setting the

parameter.

4.0 Using programming source code to setting Source address or Destination address.

If we want to use coding to send the command to SKXBee, we have to ensure the

hardware connection between SKXBee to microcontroller is complete. It can refer back

to the previous sub topic on 2.0 Xbee/XBee Pro hardware interface with microcontroller.

Due to this case, we are using SK40C and 40 pins PIC16877A to interface with SKXBee.

UART data flow will be use for them to communicate each other. So that, we will

initialize the UART configuration in programming code. This figure below has been

shown as an example code:

void uart_init(void)

{

SPBRG=129; //set baud rate as 9600 baud

BRGH=1; //baud rate high speed option

TXEN=1; //enable transmission

TX9 =0; //8-bit transmission

RX9 =0; //8-bit reception

CREN=1; //enable reception

SPEN=1; //enable serial port

}

UART Transmit and Receive coding configuration:

unsigned char uart_rec(void) //receive uart value

{

unsigned int rec_data;

while(RCIF==0); //wait for data

rec_data = RCREG;

return rec_data; //return the data received

}

void uart_send(unsigned char data)

{

while(TXIF==0); //only send the new data after

TXREG=data; //the previous data finish sent

}

void uart_str(const char *s)

{

while(*s)uart_send(*s++); // UART sending string

}

Now, we can write the coding to send command for setting SKXBee Source address and

Destination address. However, we have to refer the AT Command Mode table. The main reason

is the command code exactly same with the code we have using X-CTU software for setting the

parameter.

For initialize the Source address and Destination address to SKXBee1 module, we can

write the coding in void main() code as:

void xbee_init(void)

{

uart_str("+++");//send command to enter XBee Pro command mode

delay_ms(200);// waiting for finish sending and XBee respond

uart_str("atmy1111");//send command to setting Source address

uart_send(0xD);// 0XD is hexa code of "Enter"key

delay_ms(200);

uart_str("atwr");// send "WR" (write)command to SKXBee

uart_send(0xD);//0XD is hexa code of "Enter" key

delay_ms(200);

uart_str("atdl2222");// send command to setting Destination address

uart_send(0xD);//0XD is hexa code of "Enter" key

delay_ms(200);

uart_str("atwr");//send "WR" (write)command to SKXBee

uart_send(0xD);//0XD is hexa code of "Enter" key

delay_ms(200);

uart_str("atcn");// send command for Exit AT Command Mode

uart_send(0xD);//0XD is hexa code of "Enter" key

delay_ms(200);

}

For initialize the Source address and Destination address to SKXBee2 module, we can

write the coding in another microcontroller PIC source code void main() as:

void xbee_init(void)

{

uart_str("+++");//send command to enter XBee Pro command mode

delay_ms(200);// waiting for finish sending and XBee respond

uart_str("atmy2222");//send command to setting Source address

uart_send(0xD);// 0XD is hexa code of "Enter" key

delay_ms(200);

uart_str("atwr");// send "WR" (write)command to SKXBee

uart_send(0xD);//0XD is hexa code of "Enter" key

delay_ms(200);

uart_str("atdl1111");// send command to setting Destination address

uart_send(0xD);//0XD is hexa code of "Enter" key

delay_ms(200);

uart_str("atwr");//send "WR" (write)command to SKXBee

uart_send(0xD);//0XD is hexa code of "Enter" key

delay_ms(200);

uart_str("atcn");// send command for Exit AT Command Mode

uart_send(0xD);//0XD is hexa code of "Enter" key

delay_ms(200);

}

Using UIC00B programmer to loading source code into PIC16F877A SK40C:

When we have finished load the coding into PIC, we should press RESET button to

ensure the address will store in Xbee/XBee Pro module. Otherwise, the Xbee/XBee Pro

will store with previously address value.

NOTE: Please remember the Source Address and Destination address only need one time

setting process for ID address, the Xbee/XBee Pro module will store the address in

module. User no need to setting it every time when using Xbee/XBee module, except

that user want to change a new Source address or Destination address to these RF

module.

7.0 Conclusion:

XBee/XBee Pro is a user friendly RF module for wireless communication between two PICs or

between a PIC and a computer. When we know how to use it with wisely, we can use this

wireless device to control a robot or equipment, data collection, security system and etc. By the

way, we have to know the command protocol for this RF module, then we can used and handle it

easily with microcontroller or computer. Please do post your inquiry in our technical forum as we

seldom check the comment section in tutorial site.