Telegesis (UK) Limited
TG-ETRXn-UG-01-103
16
User Guide
1.04
ETRX1 and ETRX2
©2008 Telegesis (UK) Ltd
ETRXn User Guide (Rev 1.04)
Figure 11. Examples of received messages
4.6 Channels
A unicast has a maximum payload of 65 bytes, so if you want to send more than that, or if you
want to send continuous data in both directions, a so-called channel is needed.
To the outside world a channel appears like a wireless RS232 cable replacement, but please note
that you should not expect high data-rates, as ZigBee
®
has been designed for sensor and control
applications for distributed networks rather than for high data throughput. When using a channel
you need to implement XON/XOFF or hardware handshaking, otherwise you will risk losing data
due to a buffer overflow.
To open a channel use the “AT+OPCHAN:” command followed by the serial number of the device
to which you want to open that
channel. Alternatively you can use the “Open” button in the
“Channel” section of the Telegesis Terminal Software. By default the remote node will
automatically accept the channel if bit C of S6 is cleared.
Where bit C of S6 is set, the user on the remote end will be prompted that a channel has been
requested and will need to acknowledge the channel using the “AT+ACKCHAN:<EUI64>”
command (“Accept” button), where EUI64 is the ID of the unit which has requested the channel.
Accepting the channel produces the response “OPEN” on both ends. Once a channel has been
established, data can be sent bi-
directionally. To close the channel send “+++” on either end
(“Close” button).
Notes:
This implies that “+++” must never be part of the message payload.
“AT+OPLCHAN:xxxx,<EUI64>“ has a similar effect, but the channel automatically closes after xxxx
bytes have been transmitted by the device opening the channel. In this case “+++” may be part of
the payload, which can also contain control characters such as <CR>, <LF> and <XOFF>.
Figure 12 shows a sequence of messages when using a channel.
Heavy text
is the data entered
at the keyboard, normal text is the responses. Note that the channel is bidirectional, and there is
no local echo of the data (since it would be indistinguishable from data received).
