Telegesis (UK) Limited
TG-ETRXn-UG-01-103
15
User Guide
1.04
ETRX1 and ETRX2
©2008 Telegesis (UK) Ltd
ETRXn User Guide (Rev 1.04)
As each node hearing a broadcast within the specified amount of hops is also repeating it three
times it becomes obvious that broadcasts are consuming a lot of bandwidth. Because of this the
ZigBee
®
specification limits the amount of broadcasts which can be used to a total of 8 in every 8
seconds.
The maximum number of hops a broadcast can bridge is 10 hops.
4.3 Raw data
If you need to send data as rapidly as possible at the expense of some reliability and security, you
can broadcast it using the AT+RDATAB command. Up to 114 bytes can be sent in a packet that
bypasses the ZigBee layers of the protocol stack, and hence has no encryption or error checking.
“AT+RDATAB:xx” is similar in format to “AT+BCASTB:xx,nn”.
4.4 Unicasts
“AT+UCAST:<EUI64>,<data>“ and “AT+UCASTB:xx,<EUI64>“ function in a similar way to their
broadcast equivalents. However, the data is only sent to the specified node and “ACK” or “NACK”
is sent to the sender‟s serial port. Note that “NACK” may result from a positive “ACK” response
being lost in transmission.
To allow for multiple messages in flight, a transmission number is issued when successfully
sending a unicast and at this point it is possible to make further transmissions. The follow-on ACK
or NACK prompt is also followed by that transmission number.
In case you prefer to wait until the ACK or NACK has been received simply set bit D of S06 and no
transmission number will be issued. Instead the response will be either
“OK” if an ACK has been
received, or an error code where a NACK has been received or no feedback was received at all.
4.5 S-Casts
A sink is a node intended as a central receiver of data. In previous versions of the firmware the
coordinator and the sink used to be the same device, but with EmberZNet2.x the coordinator is
allowed to leave the network after starting it. A separate node can be selected to operate as a
data sink. A node may be changed to be a sink by setting bit 8 of S-register S06. Please note that
there should be only one single sink in the network.
In order to send data to the network‟s sink an individual node needs to know the sink's address.
This can be done by searching for a sink using the “AT+SSINK” command, alternatively the sink
can ad
vertise its services in regular intervals as set by the sink‟s S19 and S1A (see explanation of
the built-in functionality in section 5.5).
If a sink is known “AT+SCAST:<data>” sends a message to the sink and returns “ACK” or “NACK”
as with a unicast. S-casts have the advantage that the identity of the sink does not need to be
known by the user.
“AT+BCASTB”, “AT+SCASTB” allows the sending of a predefined number of characters including
<CR>, <BS>, …
There can be only one sink in a network. If an existing sink receives a message that another node
has declared itself also to be a sink, the first sink‟s function is cancelled and the relevant register
bit (S06, bit 8) is cleared.
