Overview Design notes
XBee/XBee-PRO ZigBee RF Modules User Guide 18
Design notes
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 a 1uF and 8.2pF capacitor are recommended to be placed
as near to pin1 on the PCB as possible. If using a switching regulator for your power supply, switching frequencies
above 500 kHz are preferred. Power supply ripple should be limited to a maximum 50 mV peak to peak.
Note For designs using the programmable modules an additional 10uF decoupling cap is recommended near
pin 1 of the module. The nearest proximity to pin 1 of the 3 caps should be in the following order: 8.2pf,
1uF followed by 10uF.
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 Commissioning pushbutton and associate LED on page 85 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.
36 (SIF_MOSI) Connected to pin 4 on 2x5 SIF header.
37 (SIF_LOAD) Connected to pin 7 on 2x5 SIF header.
40 (GPIO 16)
7
41 (GPIO 15)
6
42 (GPIO 14)
9
43 (GPIO 13)
11
1. These lines may not go to the external XBee pins of the module if the programmable secondary processor is populated.
EM250 Pin Number XBee Pin Number Other Usage
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