Technical Manual

56
Software
4.4. Adcon Packet Radio Protocol
The A733 is basically intended as an end device in a radio network. Most frames de-
fined by the Adcon Packet Radio Protocol are recognized and answered by an A733;
a complete list is provided (see “Frame Types” on page 59). In addition, full source
routing of frames for other destinations is implemented.
Figure 30. State Transition Diagram of the radio communication task.
4.4.1. Digital Squelch
In order to reduce the power consumption during receive mode, the unit uses a pro-
tocol developed by Adcon Telemetry for the A730 family, but with some additional
refinements to further reduce the power consumption. The receiver is pulsed at a
0.5 seconds interval. At wake-up, the receiver samples first the RF channel for a car-
rier, by measuring the RSSI. The RSSI output is extremely stable due to the wide dy-
namic range that the IF chip exhibits (over 100 dB, temperature compensated). If the
sampled RSSI is under a preset threshold, the unit will immediately go back to sleep.
This procedure takes under 20 mS, typically (from wake-up to result).
If, however, an RF level superior to the preset threshold is detected, the micropro-
cessor will try to detect a valid header, which is composed of a 2 kHz tone of at least
0.5 seconds long. The tone detection is performed by the microcontroller in soft-
Idle
Measure RF
Check
Destination
No Signal
0.5 sec
Interrupt
Header Detected
Not for us
Get Frame
We are called
New Frame Possible
Wait
Nhops + 1 s
and
Hunt Syncs
Timeout Expired
Answer
Appropriately
Ack
Resend
Frame with
Long
Header
Frame Sent Twice
No Ack
Payload is for us
Must route
Update
Header
and Send
Ack
No Ack