User Manual

XBee®/XBee‐PRO®ZBRFModules
©2011DigiInternational,Inc. 15
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 30k internal pull-up
resistors using the PR software command. No specific treatment is needed for unused outputs.
For applications that need to ensure the lowest sleep current, inputs should never be left floating. Use internal
or external pull-up or pull-down resistors, or set the unused I/O lines to outputs.
Other pins may be connected to external circuitry for convenience of operation including the Associate LED pin
(pin 15) and the Commissioning pin (pin 20). The Associate LED pin will flash differently depending on the
state of the module to the network, and a pushbutton attached to pin 20 can enable various join functions
without having to send UART commands. Please see the commissioning pushbutton and associate LED section
in chapter 7 for more details. The source and sink capabilities are limited to 4mA for all pins on the module.
The VRef pin (pin 14) is not used on this module. For compatibility with other XBee modules, we recommend
connecting this pin to a voltage reference if analog sampling is desired. Otherwise, connect to GND.
Board Layout
XBee modules do not have any specific sensitivity to nearby processors, crystals or other PCB components.
Other than mechanical considerations, no special PCB placement is required for integrating XBee radios except
for those with integral antennas. In general, Power and GND traces should be thicker than signal traces and be
able to comfortably support the maximum currents.
The radios are also designed to be self sufficient and work with the integrated and external antennas without
the need for additional ground planes on the host PCB. However, considerations should be taken on the choice
of antenna and antenna location. Metal objects that are near an antenna cause reflections and may reduce the
ability for an antenna to efficiently radiate. Using an integral antenna (like a wire whip antenna) in an enclosed
metal box will greatly reduce the range of a radio. For this type of application an external antenna would be a
better choice.
External antennas should be positioned away from metal objects as much as possible. Metal objects next to
the antenna or between transmitting and receiving antennas can often block or reduce the transmission
distance. Some objects that are often overlooked are metal poles, metal studs or beams in structures,
concrete (it is usually reinforced with metal rods), metal enclosures, vehicles, elevators, ventilation ducts,
refrigerators and microwave ovens.
The Wire Whip Antenna should be straight and perpendicular to the ground plane and/or chassis. It should
reside above or away from any metal objects like batteries, tall electrolytic capacitors or metal enclosures. If
the antenna is bent to fit into a tight space, it should be bent so that as much of the antenna as possible is
away from metal. Caution should be used when bending the antenna, since this will weaken the solder joint
where the antenna connects to the module. Antenna elements radiate perpendicular to the direction they
point. Thus a vertical antenna emits across the horizon.
Chip Antennas should not have any ground planes or metal objects above or below the module at the antenna
location. For best results the module should be in a plastic enclosure, instead of metal one. It should be placed
at the edge of the PCB to which it is mounted. The ground, power and signal planes should be vacant
immediately below the antenna section (See drawing for recommended keepout area).