Digi XBee User manual

Product Manual
XBee
XBee / XBee-PRO RF
Modules
802.15.4 Protocol

XBee / XBee-PRO RF Modules 802.15.4 Product Manual
(Part number 90000982 S)
Disclaimers
Information in this document is subject to change without notice and does not represent a commitment on
the part of Digi International. Digi provides this document “as is,” without warranty of any kind, expressed
or implied, including, but not limited to, the implied warranties of fitness or merchantability for a particular
purpose. Digi may make improvements and/or changes in this manual or in the product(s) and/or the
program(s) described in this manual at any time.
Revision Date Description
A September 2008 Baseline release.
B September 2009 Updated to support to support XBee 802.15.4 and DigiMesh 900 firmware.
C November 2010 Updates.
D July 2011 Update to antenna information.
E October 2011 Changes to the 802.15.4 and Operation sections.
F January 2012 PCB antenna changes.
G March 2012 Fixed MM command content on page 48.
H August 2012‘ Editorial change.
IN/A RevisionIisnotused.
J January 2013 Removed reference to commissioning button pin 20.
K February 2013 Corrected the KY parameter information.
L May 2013 Removed incorrect API operation information.
M July 2013 Corrected parameter range on two command descriptions. Parameter
range on IS and IO were flipped. Switched them back to the correct cells in
the table.
N April 2014 Added note on page 24 and 40 calling out appropriate European CCA value
settings.
O N/A Revision O is not used.
P June 2014 Updated link from www.ero.dk to www.cept.org.
Q N/A Revision Q is not used.
R October 2014 Fixed garbled text for the description of the [NT] parameter in the NT (Node
Discover Time) Command section. Added reference to the XBee 802.15.4
Development Kit Getting Started Guide in the front matter.
S February 2015 Updated European restrictions for transmitting below 10 dBm. Updated
the warranty and certification information. Updated programming
examples section. Corrected the maximum value of the IT command.
Corrected P1 command parameters.

XBee / XBee-PRO RF Modules 802.15.4 Product Manual 3
Trademarks and copyright
Digi, Digi International, and the Digi logo are trademarks or registered trademarks in the United States and
other countries worldwide. All other trademarks mentioned in this document are the property of their
respective owners.
© 2015 Digi International. All rights reserved.
Customer support
Telephone (8:00 am — 5:00 pm CST):
US and Canada: 877.912.3444
Worldwide: +1 952.912.3456
Online: www.digi.com/support/eservice
Mail:
Digi International
11001 Bren Road East
Minnetonka, MN 55343
US
Warranty
View the product’s warranty online: http://www.digi.com/howtobuy/terms

Full book title 4
Contents
XBee®/ XBee-PRO®RF Modules
Key features of the XBee / XBee-PRO Modules 8
Worldwide acceptance 9
Specifications 9
Antenna options 11
Mechanical drawings of the XBee/XBee-PRO RF Module 11
Mounting considerations for the XBee / XBee-PRO RF Module 11
Pin signals for the XBee/XBee-PRO RF Module 12
Design notes for the XBee/XBee-PRO RF Module 13
Power supply design 13
Recommended pin connections 14
Board layout 14
Antenna performance 14
Electrical characteristics of the XBee/XBee-PRO RF Module 16
XBee/XBee-PRO RF Module operation
Serial communications for the XBee/XBee-PRO RF Module 18
UART data flow 18
Transparent operation 19
Flow control 20
ADC and Digital I/O line support of the XBee/XBee-PRO RF module 21
I/O data format 22
API support 22
Sleep support 22
DIO pin change detect 23
Sample Rate (Interval) 23
I/O line passing 23
Configuration example 24
XBee / XBee-PRO networks 24
Peer-to-peer 24
NonBeacon (with coordinator) 25
Association 25
XBee / XBee-PRO addressing 28
Unicast Mode 28
Broadcast Mode 28
Modes of operation for the XBee/XBee-PRO RF Modules 29

Full book title 5
Idle Mode 29
Transmit/Receive Modes 29
Sleep Mode 31
Command Mode 33
XBee/XBee-PRO RF Module configuration
Programming the RF Module 36
Programming examples 36
Remote configuration commands 40
Sending a remote command 40
Applying changes on remote 40
Remote command responses 40
Command reference tables 40
Special 41
Networking and security 41
RF interfacing 49
Sleep (low power) 50
Serial interfacing 51
I/O settings 52
Diagnostics 55
AT command options 56
Command descriptions for the XBee/XBee-PRO RF Module 57
A1 (End Device association) command 57
A2 (Coordinator Association) command 58
AC (Apply Changes) command 59
AI (Association Indication) command 59
AP (API Enable) command 60
AS (Active Scan) command 61
BD (Interface Data Rate) command 62
CA (CCA Threshold) command 63
CC (Command Sequence Character) command 63
CE (Coordinator Enable) command 64
CH (Channel) command 64
CN (Exit Command Mode) command 64
CT (Command Mode Timeout) command 65
D0 - D4 (DIOn Configuration) commands 65
D5 (DIO5 Configuration) command 66
D6 (DIO6 Configuration) command 66
D7 (DIO7 Configuration) command 67
D8 (DI8 Configuration) command 67
DA (Force Disassociation) command 68
DB (Received Signal Strength) command 68
DH (Destination Address High) command 68
DL (Destination Address Low) command 69
DN (Destination Node) command 69
DP (Disassociation Cyclic Sleep Period) command 69
EA (ACK Failures) command 70
EC (CCA Failures) command 70
ED (Energy Scan) command 70
EE (AES Encryption Enable) command 71
FP (Force Poll) command 71
FR (Software Reset) command 72
GT (Guard Times) command 72

Full book title 6
HV (Hardware Version) command 72
IA (I/O Input Address) command 72
ID (Pan ID) command 73
IO (Digital Output Level) command 73
IR (Sample Rate) command 74
IS (Force Sample) command 74
IT (Samples before TX) command 74
IU (I/O Output Enable) command 75
KY (AES Encryption Key) command 75
M0 (PWM0 Output Level) command 75
M1 (PWM1 Output Level) command 76
MM (MAC Mode) command 76
MY (16-bit Source Address) command 77
NB (Parity) command 77
ND (Node Discover) command 78
NI (Node Identifier) command 79
NO (Node Discover Options) command 79
NT (Node Discover Time) command 79
P0 (PWM0 Configuration) command 80
P1 (PWM1 Configuration) command 80
PL (Power Level) command 81
PR (Pull-up Resistor) command 81
PT (PWM Output Timeout) command 82
RE (Restore Defaults) command 82
RN (Random Delay Slots) command 82
RO (Packetization Timeout) command 82
RP (RSSI PWM Timer) command 83
RR (XBee Retries) command 83
SC (Scan Channels) command 84
SD (Scan Duration) command 85
SH (Serial Number High) command 85
SL (Serial Number Low) command 85
SM (Sleep Mode) command 86
SO (Sleep Mode command) 86
SP (Cyclic Sleep Period) command 87
ST (Time before Sleep) command 87
T0 - T7 ((D0-D7) Output Timeout) command 88
VL (Firmware Version - Verbose) 88
VR (Firmware Version) command 88
WR (Write) command 88
API Operation for the XBee/XBee-PRO RF Module 89
API frame specifications 89
API types 91
Agency certifications
United States (FCC) 98
OEM labeling requirements 98
FCC notices 98
FCC-approved antennas (2.4 GHz) 99
RF exposure 103
Europe (ETSI) 103
Approved antennas 104
Canada (IC) 105

Full book title 7
Labeling requirements 105
Japan 105
Labeling requirements 105
ANATEL (Brazil) certification 105

XBee / XBee-PRO RF Modules 802.15.4 Product Manual 8
XBee®/ XBee-PRO®RF Modules
The XBee and XBee-PRO RF Modules were engineered to meet IEEE 802.15.4 standards and support
the unique needs of low-cost, low-power wireless sensor networks. The modules require minimal
power and provide reliable delivery of data between devices.
The modules operate within the ISM 2.4 GHz frequency band and are pin-for-pin compatible with
each other.
Key features of the XBee / XBee-PRO Modules
Long range data integrity Low power
XBee
•Indoor/urban: up to 100 ft (30 m)
•Outdoor line-of-sight: up to 300 ft (90 m)
•Transmit power: 1 mW (0 dBm)
•Receiver sensitivity: -92 dBm
XBee-PRO
•Indoor/Urbaun: up to 300 ft (90 m), 200' (60 m) for
international variant
•Outdoor line-of-sight: up to 1 mile (1600 m), 2500 ft
(750 m) for international variant
•Transmit power: 63 mW (18 dBm), 10 mW (10 dBm) for
international variant
•Receiver sensitivity: -100 dBm
•RF data rate: 250,000 b/s
XBee
•TX peak current: 45 mA (@3.3 V)
•RX current: 50 mA (@3.3 V)
•Power-down current: < 10 μA
XBee-PRO
•TX peak current: 250 mA,150 mA for
international variant
•TX peak current (RPSMA module only): 340 mA,
180 mA for international variant
•RX current: 55 mA (@3.3 V)
•Power-down current: < 10 μA

Worldwide acceptance
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 9
Worldwide acceptance
FCC Approval (USA) Refer to Agency certifications on page 98 for FCC requirements.
Systems that contain XBee / XBee-PRO RF Modules inherit Digi Certifications.
Industrial, Scientific and Medical (ISM) 2.4 GHz frequency band.
Manufactured under ISO 9001:2000 registered standards
XBee / XBee-PRO RF Modules are optimized for use in US, Canada, Australia, Israel and
Europe, contact Digi for a complete list of agency approvals.
Specifications
Advanced networking and security Easy to use
Retries and acknowledgments
Direct Sequence Spread Spectrum (DSSS)
Each direct sequence channel has over 65,000 unique
network addresses available
Source/destination addressing
Unicast and broadcast communications
Supports point-to-point, point-to-multipoint and peer-to-
peer topologies
Coordinator/End Device operations
Transparent and API operations
128-bit encryption
No configuration necessary for out-of box RF
communications
Free XCTU software (testing and configuration
software)
AT and API Command Modes for configuring
module parameters
Extensive command set
Small form factor
ADC and I/O line support
Analog-to-digital conversion, digital I/O
I/O line passing
Table 1: Specifications of the XBee / XBee-PRO OEM RF Module
Specification XBee XBee-PRO
Performance
Indoor/urban range Up to 100 ft (30 m) Up to 300 ft. (90 m), up to 200 ft
(60 m) International variant
Outdoor RF line-of-sight range Up to 300 ft (90 m) Up to 1 mile (1600 m), up to 2500 ft
(750 m) international variant
Transmit power output
(software selectable)
1mW (0 dBm) 63 mW (18dBm)*
10 mW (10 dBm) for International
variant
RF data rate 250,000 b/s 250,000 b/s
Serial interface data rate
(software selectable)
1200 b/s - 250 kb/s
(non-standard baud rates also
supported)
1200 bps - 250 kb/s
(non-standard baud rates also
supported)
Receiver sensitivity -92 dBm (1% packet error rate) -100 dBm (1% packet error rate)
Power requirements
Supply voltage 2.8 - 3.4 V 2.8 - 3.4 V

Specifications
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 10
Transmit current (typical) 45 mA (@ 3.3 V) 250 mA (@3.3 V) (150 mA for
international variant) RPSMA
module only: 340 mA (@3.3 V)
(180 mA for international variant)
Idle / receive current (typical) 50 mA (@ 3.3 V) 55 mA (@ 3.3 V)
Power-down current < 10 uA < 10 uA
General
Operating frequency ISM 2.4 GHz ISM 2.4 GHz
Dimensions 0.960 in x 1.087 in (2.438cm x 2.761cm) 0.960 in x 1.297 in (2.438cm x 3.294
cm)
Operating temperature -40 to 85º C (industrial) -40 to 85º C (industrial)
Antenna options Integrated whip antenna, embedded
PCB antenna, U.FL connector, RPSMA
connector
Integrated whip antenna,
embedded PCB antenna, U.FL
connector, RPSMA connector
Networking and security
Supported network topologies Point-to-point, point-to-multipoint and
peer-to-peer
Number of channels
(software selectable)
16 direct sequence channels 12 direct sequence channels
Addressing options PAN ID, channel and addresses PAN ID, channel and addresses
Agency approvals
United States (FCC Part 15.247) OUR-XBEE OUR-XBEEPRO
Industry Canada (IC) 4214A-XBEE 4214A-XBEEPRO
Europe (CE) ETSI ETSI (Maximum 10 dBm transmit
power output)*
Japan R201WW07215214 R201WW08215111 (Maximum
10 dBm transmit power output)*
Wire, chip, RPMSA, and U.FL
versions are certified for Japan. PCB
antenna version is not.
Australia C-Tick C-Tick
Brazil ANATEL 0369-15-1209 ANATEL 0378-15-1209
*See Agency certifications on page 98 for region-specific certification requirements.
Table 1: Specifications of the XBee / XBee-PRO OEM RF Module
Specification XBee XBee-PRO

Mechanical drawings of the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 11
Antenna options
The ranges specified are typical when using the integrated whip (1.5 dBi) and dipole (2.1 dBi)
antennas. The printed circuit board (PCB) antenna option provides advantages in its form factor,
however, it typically yields shorter range than the whip and dipole antenna options when
transmitting outdoors.For more information, refer to the XBee and XBee-PRO OEM RF Module
Antenna Considerations Application Note.
Mechanical drawings of the XBee/XBee-PRO RF Module
Figure 1: Mechanical drawings of the XBee / XBee-PRO OEM RF Modules (antenna options not
shown). The XBee and XBee-PRO RF Modules are pin-for-pin compatible.
Mounting considerations for the XBee / XBee-PRO RF Module
The XBee modules are designed to mount into a receptacle (socket) and therefore do not require any
soldering when mounting them to a board. The XBee-PRO Development Kits contain RS-232 and USB
interface boards which use two 20-pin receptacles to receive modules.

Pin signals for the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 12
Figure 2: XBee-PRO Module mounting to an RS-232 interface board.
Century Interconnect manufactures the receptacles used on Digi development boards. Several other
manufacturers provide comparable mounting solutions, however, Digi currently uses the following
receptacles:
•Through-hole single-row receptacles -
Samtec P/N: MMS-110-01-L-SV (or equivalent)
•Surface-mount double-row receptacles -
Century Interconnect P/N: CPRMSL20-D-0-1 (or equivalent)
•Surface-mount single-row receptacles -
Samtec P/N: SMM-110-02-SM-S
We also recommend printing an outline of the module on the board to indicate the orientation the
module should be mounted.
Pin signals for the XBee/XBee-PRO RF Module
Figure 3: XBee / XBee-PRO RF Module pin number (top sides shown - shields are on the bottom)
Table 2: Pin assignments for the XBee-PRO Modules
(Low-asserted signals are distinguished with a horizontal line above signal name.)
Pin # Name Direction Description
1 VCC - Power supply
2 DOUT Output UART data out
3 DIN / CONFIG Input UART data In
4 DO8* Either Digital output 8
5 RESET Input Module reset (reset pulse must be at least 200 ns)
6 PWM0 / RSSI Either PWM output 0 / RX signal strength indicator

Design notes for the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 13
Notes
•Minimum connections: VCC, GND, DOUT and DIN
•Minimum connections for updating firmware: VCC, GND, DIN, DOUT, RTS and DTR
•Signal direction is specified with respect to the module
•The module includes a 50 kpull-up resistor attached to RESET
•You can configure several of the input pull-ups using the PR command
•Leave any unused pins disconnected
Design notes for the XBee/XBee-PRO RF Module
The XBee modules do not specifically require any external circuitry or specific connections for proper
operation. However, there are some general design guidelines that are recommended for help in
troubleshooting and building a robust design.
Power supply design
Poor power supply can lead to poor radio performance, especially if the supply voltage is not kept
within tolerance or is excessively noisy. To help reduce noise, we recommend placing a 1.0 μF and 8.2
pF capacitor as near as possible to pin 1 on the XBee. If using a switching regulator for the power
supply, switching frequencies above 500 kHz are preferred. Power supply ripple should be limited to
a maximum 100 mV peak to peak.
7 PWM1 Either PWM output 1
8 [reserved] - Do not connect
9DTR
/ SLEEP_RQ/ DI8 Either Pin sleep control line or digital input 8
10 GND - Ground
11 AD4 / DIO4 Either Analog input 4 or digital I/O 4
12 CTS / DIO7 Either Clear-to-send flow control or digital I/O 7
13 ON / SLEEP Output Module status indicator
14 VREF Input Voltage reference for A/D inputs
15 Associate / AD5 / DIO5 Either Associated indicator, analog input 5 or digital I/O 5
16 RTS / DIO6 Either Request-to-send flow control, or digital I/O 6
17 AD3 / DIO3 Either Analog input 3 or digital I/O 3
18 AD2 / DIO2 Either Analog input 2 or digital I/O 2
19 AD1 / DIO1 Either Analog input 1 or digital I/O 1
20 AD0 / DIO0 Either Analog input 0, digital IO 0
* Function is not supported at the time of this release
Table 2: Pin assignments for the XBee-PRO Modules
(Low-asserted signals are distinguished with a horizontal line above signal name.)
Pin # Name Direction Description

Design notes for the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 14
Recommended pin connections
The only required pin connections are VCC, GND, DOUT and DIN. To support serial firmware updates,
VCC, GND, DOUT, DIN, RTS, and DTR should be connected.
All unused pins should be left disconnected. All inputs on the radio can be pulled high with internal
pull-up resistors using the PR software command. No specific treatment is needed for unused
outputs.
Other pins may be connected to external circuitry for convenience of operation including the
Associate LED pin (pin 15). The Associate LED will flash differently depending on the state of the
module.
If analog sampling is desired, VRef (pin 14) should be attached to a voltage reference.
Board layout
XBee modules are designed to be self sufficient and have minimal sensitivity to nearby processors,
crystals or other PCB components. As with all PCB designs, Power and Ground traces should be
thicker than signal traces and able to comfortably support the maximum current specifications. No
other special PCB design considerations are required for integrating XBee radios except in the
antenna section.
Antenna performance
Antenna location is an important consideration for optimal performance. In general, antennas
radiate and receive best perpendicular to the direction they point. Thus a vertical antenna's radiation
pattern is strongest across the horizon. Metal objects near the antenna may impede the radiation
pattern. Metal objects between the transmitter and receiver can block the radiation path or reduce
the transmission distance, so antennas should be positioned away from them when possible. Some
objects that are often overlooked are metal poles, metal studs or beams in structures, concrete (it is
usually reinforced with metal rods), vehicles, elevators, ventilation ducts, refrigerators, microwave
ovens, batteries, and tall electrolytic capacitors. If the XBee is to be placed inside a metal enclosure,
an external antenna should be used.
XBee units with the Embedded PCB Antenna should not be placed inside a metal enclosure or have
any ground planes or metal objects above or below the antenna. For best results, place the XBee at
the edge of the host PCB on which it is mounted. Ensure that the ground, power and signal planes
are vacant immediately below the antenna section. We recommend allowing a “keepout” area, which
is shown in detail on the next page.

Design notes for the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 15

Electrical characteristics of the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 16
Electrical characteristics of the XBee/XBee-PRO RF Module
Table 3: DC Characteristics (VCC = 2.8 - 3.4 VDC)
Symbol Characteristic Condition Min Typical Max Unit
VIL Input Low Voltage All Digital Inputs --
0.35 * VCC V
VIH Input High Voltage All Digital Inputs 0.7 * VCC --V
VOL Output Low Voltage IOL = 2 mA, VCC >= 2.7
V--0.5V
VOH Output High Voltage IOH = -2 mA, VCC >=
2.7 V
VCC - 0.5 --V
IIIN Input Leakage Current VIN = VCC or GND, all
inputs, per pin -0.0251μA
IIOZ High Impedance
Leakage Current
VIN = VCC or GND, all
I/O High-Z, per pin -0.0251μA
TX Transmit current VCC = 3.3 V -45
(XBee)
215, 140
(PRO, Intl) -mA
RX Receive Current VCC = 3.3 V -50
(XBee) 55 (PRO) - mA
PWR-DWN Power-down Current SM parameter = 1 -<10 -μA
Table 4: ADC characteristics (operating)
Symbol Characteristic Condition Min Typical Max Unit
VREFH VREF - analog-to-digital converter
reference range
2.08 - VDDAD* V
IREF VREF - reference supply current Enabled - 200 - μA
Disabled or Sleep Mode - < 0.01 0.02 μA
VINDC Analog input voltage** VSSAD - 0.3 - VDDAD + 0.3 V
* VDDAD is connected to VCC.
** Maximum electrical operating range, not valid conversion range.
Table 5: ADC timing/performance characteristics1
Symbol Characteristic Condition Min Typical Max Unit
RAS Source impedance at input2-- 10k
VAIN Analog input voltage3VREFL VREFH V
RES Ideal resolution (1 LSB)42.08V < VDDAD < 3.6V 2.031 - 3.516 mV
DNL Differential non-linearity5- ±0.5 ±1.0 LSB

Electrical characteristics of the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 17
INL Integral non-linearity6- ±0.5 ±1.0 LSB
EZS Zero-scale error7- ±0.4 ±1.0 LSB
FFS Full-scale error8- ±0.4 ±1.0 LSB
EIL Input leakage error9- ±0.05 ±5.0 LSB
ETU Total unadjusted error10 - ±1.1 ±2.5 LSB
1. All accuracy numbers are based on the processor and system being in WAIT state (very little activity and no
IO switching) and that adequate low-pass filtering is present on analog input pins (filter with 0.01 μF to 0.1 μF
capacitor between analog input and VREFL). Failure to observe these guidelines may result in system or
microcontroller noise causing accuracy errors which will vary based on board layout and the type and
magnitude of the activity. Data transmission and reception during data conversion may cause some
degradation of these specifications, depending on the number and timing of packets. We advise testing the
ADCs in your installation if best accuracy is required.
2. RAS is the real portion of the impedance of the network driving the analog input pin. Values greater than this
amount may not fully charge the input circuitry of the ATD resulting in accuracy error.
3. Analog input must be between VREFL and VREFH for valid conversion. Values greater than VREFH will convert to
$3FF.
4. The resolution is the ideal step size or 1LSB = (VREFH–VREFL)/1024.
5. Differential non-linearity is the difference between the current code width and the ideal code width (1LSB).
The current code width is the difference in the transition voltages to and from the current code.
6. Integral non-linearity is the difference between the transition voltage to the current code and the adjusted
ideal transition voltage for the current code. The adjusted ideal transition voltage is (Current Code–1/2)*(1/
((VREFH+EFS)–(VREFL+EZS))).
7. Zero-scale error is the difference between the transition to the first valid code and the ideal transition to that
code. The Ideal transition voltage to a given code is (Code–1/2)*(1/(VREFH–VREFL)).
8. Full-scale error is the difference between the transition to the last valid code and the ideal transition to that
code. The ideal transition voltage to a given code is (Code–1/2)*(1/(VREFH–VREFL)).
9. Input leakage error is error due to input leakage across the real portion of the impedance of the network
driving the analog pin. Reducing the impedance of the network reduces this error.
10.Total unadjusted error is the difference between the transition voltage to the current code and the ideal
straight-line transfer function. This measure of error includes inherent quantization error (1/2LSB) and
circuit error (differential, integral, zero-scale, and full-scale) error. The specified value of ETU assumes zero
EIL (no leakage or zero real source impedance).
Table 5: ADC timing/performance characteristics1
Symbol Characteristic Condition Min Typical Max Unit

XBee / XBee-PRO RF Modules 802.15.4 Product Manual 18
XBee/XBee-PRO RF Module operation
Serial communications for the XBee/XBee-PRO RF Module
The XBee / XBee-PRO RF Modules interface to a host device through a logic-level asynchronous serial
port. Through its serial port, the module can communicate with any logic and voltage compatible
UART; or through a level translator to any serial device. For example: Through a Digi proprietary RS-
232 or USB interface board.
UART data flow
Devices that have a UART interface can connect directly to the pins of the RF module as shown in the
figure below.
Figure 4: System data flow diagram in a UART-interfaced environment
(Low-asserted signals distinguished with horizontal line over signal name.)
Serial data
Data enters the module UART through the DI pin (pin 3) as an asynchronous serial signal. The signal
should idle high when no data is being transmitted.
Each data byte consists of a start bit (low), 8 data bits (least significant bit first) and a stop bit (high).
The following figure illustrates the serial bit pattern of data passing through the module.

Serial communications for the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 19
Figure 5: UART data packet 0x1F (decimal number "31") as transmitted through the RF module
Example Data Format is 8-N-1 (bits - parity - # of stop bits)
Serial communications depend on the two UARTs (the microcontroller's and the RF module's) to be
configured with compatible settings (baud rate, parity, start bits, stop bits, data bits).
The UART baud rate and parity settings on the XBee module can be configured with the BD and NB
commands, respectively. See Command reference tables on page 40 for details.
Transparent operation
By default, XBee / XBee-PRO RF Modules operate in Transparent Mode. When operating in this mode,
the modules act as a serial line replacement - all UART data received through the DI pin is queued up
for RF transmission. When RF data is received, the data is sent out the DO pin.
Serial-to-RF packetization
Data is buffered in the DI buffer until one of the following causes the data to be packetized and
transmitted:
1. No serial characters are received for the amount of time determined by the RO (Packetization
Timeout) parameter. If RO = 0, packetization begins when a character is received.
2. The maximum number of characters that will fit in an RF packet (100) is received.
3. The Command Mode Sequence (GT + CC + GT) is received. Any character buffered in the DI buffer
before the sequence is transmitted.
If the module cannot immediately transmit (for instance, if it is already receiving RF data), the serial
data is stored in the DI Buffer. The data is packetized and sent at any RO timeout or when 100 bytes
(maximum packet size) are received.
If the DI buffer becomes full, hardware or software flow control must be implemented in order to
prevent overflow (loss of data between the host and module).
API operation
API (Application Programming Interface) Operation is an alternative to the default Transparent
Operation. The frame-based API extends the level to which a host application can interact with the
networking capabilities of the module.
When in API mode, all data entering and leaving the module is contained in frames that define
operations or events within the module.
Transmit data frames (received through the DI pin (pin 3)) include:
•RF Transmit data frame
•Command frame (equivalent to AT commands)
Receive Data frames (sent out the DO pin (pin 2)) include:

Serial communications for the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 20
•RF-received data frame
•Command response
•Event notifications such as reset, associate, disassociate, and so forth
The API provides alternative means of configuring modules and routing data at the host application
layer. A host application can send data frames to the module that contain address and payload
information instead of using command mode to modify addresses. The module will send data frames
to the application containing status packets; as well as source, RSSI and payload information from
received data packets.
The API operation option facilitates many operations such as the examples cited below:
•Transmitting data to multiple destinations without entering Command Mode
•Receive success/failure status of each transmitted RF packet
•Identify the source address of each received packet
To implement API operations, refer to API Operation for the XBee/XBee-PRO RF Module on page 89.
Flow control
Figure 6: Internal data flow diagram
DI (Data In) buffer
When serial data enters the RF module through the DI pin (pin 3), the data is stored in the DI Buffer
until it can be processed.
Hardware Flow Control (CTS). When the DI buffer is 17 bytes away from being full; by default, the
module de-asserts CTS (high) to signal to the host device to stop sending data [refer to D7 (DIO7
Configuration) parameter]. CTS is re-asserted after the DI Buffer has 34 bytes of memory available.
To eliminate the need for flow control:
1. Send messages that are smaller than the DI buffer size (202 bytes).
2. Interface at a lower baud rate [BD (Interface Data Rate) parameter] than the throughput data rate.
Case in which the DI Buffer may become full and possibly overflow:
If the module is receiving a continuous stream of RF data, any serial data that arrives on the DI pin is
placed in the DI Buffer. The data in the DI buffer will be transmitted over-the-air when the module is
no longer receiving RF data in the network.
Refer to the RO (Packetization Timeout), BD (Interface Data Rate) and D7 (DIO7 Configuration)
command descriptions for more information.