Digi XBee 3 802.15.4, User Manual

Page: 99 / 264

I/O support Periodic I/O sampling
Digi XBee® 3 802.15.4 RF Module User Guide 99
n
To disable periodic sampling, set IR to 0 .
n
For all other IR values, the device samples data when IR milliseconds elapse and transmits the
sampled data to the destination address.
The DH (Destination Address High) and DL (Destination Address Low) commands determine the
destination address of the I/O samples. You must configure at least one pin as a digital I/O or ADC
input on the sending node to generate sample data.
Destination
If the receiving device is operating in API operating mode the I/O data sample is emitted out of the
serial port. Devices that are in Transparent operating mode discard the I/O data samples they receive
unless you enable line passing.
I/O sampling upon wake
By default, a device that is configured for sleep ( SM > 0 ) that has at least one digital I/O or ADC
enabled transmits an I/O sample upon wake regardless of how IR is configured. Sampling upon wake
can be disabled by clearing bit 1 of the SO . For more information about setting sleep modes, see Sleep
modes and SO (Sleep Options) .
Multiple samples per packet
IT (Samples before TX) specifies how many I/O samples can be transmitted in a single OTA packet. Any
single-byte value (0 - 0xFF) is accepted for input. However, the value is adjusted downward based on
how many I/O samples can fit into a maximum size packet; see
Maximum payload . A query of IT after
changes are applied tells how many I/O samples will actually be gathered.
Since MM (MAC Mode) must be 0 or 3 to send I/O samples, the maximum payload in the best of
conditions (short source address, short destination address, and no encryption) is 114 bytes. Seven of
those bytes are used by the command header and the I/O header, leaving 107 bytes for I/O samples.
The minimum I/O sample is 2 bytes. Therefore the maximum possible usable value for
IT is 53 (or
0x35 ).
Only legacy I/O frames allow for gathering multiple samples. If you set AO to 0 or 1 , then IT is not
applicable and only one sample can be gathered per frame.
Example: Remote AT command in API mode
A device is configured with the following settings:
n
D0 and D1 are set to ADC ( 2 )
n
D3 is configured as a digital input ( 3 )
n
AO is set to 2 , so legacy frames are generated
n
IT is configured to 3 , so that three samples are gathered per transmission
On the destination node, the following frame is emitted:
7E 00 1A 83 12 34 26 02 03 06 04 00 04 01 28 03 12 00 00 01 58 02 FE 00 04 01 2A 03 A0 94