Specifications

I
2
C
Two IO pins can optionally function as an I
2
C bus. IO11 becomes SCL, and IO10 becomes SDA. Use
external pull-up resistors to VCC. Resistors on the order of 10 KΩ work well.
Memory Usage
SNAP Protocol Memory Usage:
Global Buffer Pool: 7
UART Budget: 4
Mesh Routing Budget: 4
RPC Budget: 4
Radio Budget: 4
STDOUT Budget: 2
SNAPpy Virtual Machine Memory Usage:
Number of Tiny Strings: 7
Tiny String Size: up to 8 characters
Number of Medium Strings: 6
Medium String Size: up to 62 characters
Global Variables: 64
Concurrent Local Variables: 64
Maximum Call Stack Depth: 8
Platform-Specific SNAPpy Functionality
900 MHz Channel usage:
FCC rules for FHSS radios in the 900 MHz range require that the transmitting radio hop across
multiple frequencies rather than performing all its transmissions on a single frequency. FHSS SNAP
modules based on the Si100x select a range of 25 frequencies from the 66 available, based on the
channel specified for the node (in NV parameter 4), and hop amongst those 25 frequencies.
Adjacent SNAP channels will have overlap in the frequencies in use with FHSS firmware, but
interference will be minimized by the frequency hopping. There will not be any cross-channel
communications: Even though nodes on different channels may be sharing some subset of frequencies,
they will not “hear” each others’ communications.
Consult the getChannel() function for details about which channels and frequencies are used.
If your operating environment has issues with noise and interference in the 900 MHz range, you may
find that changing to a different channel (which provides a different pool of 25 frequencies) reduces or
eliminates the interference.
SNAP Reference Manual Document Number 600-0007K Page 167 of 202