Specifications

characters. The CTS pin goes high (temporarily) if the RFE is “full” and cannot accept any more
characters (you can keep sending characters, but they will likely be dropped).
When flow control is ON (isEnabled = True) and isTxEnable is also True, the CTS pin functions as a
TXENA signal. The CTS pin is normally high. It transitions low before any characters are transmitted,
and remains low until they have been completely sent. Only then does the CTS pin transition back
high.
NOTE – It is important to realize that UART handshake lines are active-low. A low voltage level on
the CTS pin is a boolean “False.” but actually means that it is “Clear To Send.” A high voltage level
on the CTS pins is a boolean “True,” but actually means it is not “Clear To Send.” RTS behaves
similarly.
This function returns no value.
getChannel() – Get which channel the node is on
The getChannel() function returns a number representing which SNAP channel the node is currently
on. For SNAP devices operating in the 2.4 GHz range, the number will be in the 0-15 range. For 900
MHz devices running the FHSS (frequency-hopping) firmware, the number should be in the 0-15
range, but could be in the 0-65 range. (See the getEnergy() function for more details about frequency
distribution under FHSS firmware.)
For nodes operating in the 2.4 GHz range, SNAP channel 0 corresponds to 802.15.4 channel 11, 1 to
12, and so on.
SNAP
Channel
802.15.4
Channel
SNAP
Channel
802.15.4
Channel
SNAP
Channel
802.15.4
Channel
SNAP
Channel
802.15.4
Channel
0 11 4 15 8 19 12 23
1 12 5 16 9 20 13 24
2 13 6 17 10 21 14 25
3 14 7 18 11 22 15 26
For nodes operating in the 900 MHz range with FHSS (frequency-hopping) firmware, getChannel()
returns an indication of which range of frequencies is in use by the node.
Radios with FHSS firmware “hop” between a minimum of 25 frequencies to avoid saturating any one
frequency with too much transmission energy. Usable frequencies begin at 902 MHz and continue in
0.4 MHz increments through 928 MHz. SNAP selects 25 consecutive frequencies based on the
“channel” specified by the user, skipping the first and last frequencies in the overall band. When the
selected range would span past the last available frequency, SNAP wraps around to the beginning of
the frequency range, so that if you have interference within part of the 900 MHz band in your
environment you can select a channel that provides frequencies that avoid the interference.
The following table shows the frequency range in use by each SNAP channel with FHSS firmware.
Page 48 of 202 SNAP Reference Manual Document Number 600-0007K