Specifications

868 MHz Channel usage:
Si100x radios operating in the 868 MHz range share the same pool of three frequencies regardless of
the radio channel specified. Controls within the SNAP firmware prevent communications from
bleeding across channels.
Carrier Sense (NV Parameter 16) and Collision Detect (NV Parameter 17):
The default values for Carrier Sense (NV Parameter 16) and Collision Detect (NV Parameter 17) are
disabled. (This is true for all SNAP platforms.) Enabling Carrier Sense or Collision Detect can
increase the reliability of multicast messaging, but may provide a performance hit. If you wish to
enable these abilities, you may want to adjust Silicon Labs’ default value for the RSSI Threshold for
Clear Channel Indicator, which you can do with the pokeRadio(0x27, value) command, to
meet the needs of your network and environment.
Setting the value too low will cause SNAP to interpret noise as interference and needlessly rebroadcast
multicast packets. In a worst-case scenario, the node may get stuck rebroadcasting hundreds or
thousands of times before it can receive or transmit any other radio traffic. Silicon Labs’ default value
for the register is 30 (0x1E), and higher values make the radio accept a higher noise floor before
indicating that a transmission has been compromised. The SNAP firmware defaults the value to 65.
Reference the manufacturer’s documentation for more details.
Maximum Loyalty (NV Parameter 53):
The requirement for channel hopping in the 900 MHz FHSS firmware means that a listening radio will
constantly be scanning the available frequencies to listen for transmissions from other nodes on the
same channel. Because the frequency hopping order is defined, after sending or receiving a
transmission a node will know where to expect the next transmission. It will wait, listening on that
frequency, for the duration of the Maximum Loyalty period (in milliseconds) before resuming its scan
of all frequencies.
If a node is broadcasting sequential packets, it will assume that the receiving radio will be expecting
its next packet on a defined frequency and will broadcast its next packet with a shorter preamble,
allowing for faster data throughput. If a node sends a broadcast and is expecting a reply, it will
likewise wait on that next hop frequency for that reply for the duration of the loyalty period before
resuming a scan of all channels.
The default value of 185 is an optimized value for most environments. If you modify this parameter,
be sure to set it to the same value for all nodes in your network. Setting the value to 0 means that no
node will ever delay before scanning all channels when listening for messages, and that no
transmitting node will ever transmit packets with a shorter preamble.
Clock Regulator (NV Parameter 65):
For Si100x implementations that do not have an external crystal to control RTC and sleep timing, NV
Parameter 65 allows you to regulate the internal clock somewhat to adjust for differences in your
hardware and your environment. For most accurate timing, you may need to adjust this value
depending on the ambient temperature and the operating voltage of your node. The range for the value
is 0-15, and the default value is 8. The change takes effect only after rebooting.
This parameter has no effect if you have an external crystal controlling your sleep timing.
Page 168 of 202 SNAP Reference Manual Document Number 600-0007K