AeroComm Corporation 44249AJ Manuale Utente
5
5
5
5////8/2007
8/2007
8/2007
8/2007
33
33
33
33
5.2.3
5.2.3
5.2.3
5.2.3 Random Back Off
Random Back Off
Random Back Off
Random Back Off
Random Back Off
Random Back Off
Random Back Off
Random Back Off – If multiple AC4424 transceivers try to send packets out over the RF at
the exact same time, the packets will collide and will not be received by the intended
receiver. In fact, if after a collision occurs, both transceivers retry at the same time, the retry
will also fail. To avoid further collisions, a transceiver can be programmed to wait a random
number of packet times (hops) before resending its data. The amount of randomness is
controlled by this parameter and this feature is not valid in broadcast mode. Keep in mind
that selecting a larger value for Random Back Off will increase the overall latency of the
AC4424. The latency calculation becomes:
the exact same time, the packets will collide and will not be received by the intended
receiver. In fact, if after a collision occurs, both transceivers retry at the same time, the retry
will also fail. To avoid further collisions, a transceiver can be programmed to wait a random
number of packet times (hops) before resending its data. The amount of randomness is
controlled by this parameter and this feature is not valid in broadcast mode. Keep in mind
that selecting a larger value for Random Back Off will increase the overall latency of the
AC4424. The latency calculation becomes:
Worst Case Latency = 8ms Hop * # of retries * Maximum Random Value
[multiply by 16ms if using Full Duplex mode]
Latency is a very important consideration when using a wireless device. The AC4424 has a
256 byte interface buffer. If, due to latency, the radio cannot send the data out over the RF
as fast as data is coming into the radio over the serial interface, the buffer will eventually fill
up. If data continues coming into the radio once the buffer is full, the buffer will overflow and
the new incoming data will be lost. It is strongly recommended that the radio host monitor
the CTS pin to avoid this situation. The transceiver asserts this pin high as the buffer is filling
to signal the OEM Host to stop sending data. The transceiver will take CTS Low once the
buffer becomes less full.
256 byte interface buffer. If, due to latency, the radio cannot send the data out over the RF
as fast as data is coming into the radio over the serial interface, the buffer will eventually fill
up. If data continues coming into the radio once the buffer is full, the buffer will overflow and
the new incoming data will be lost. It is strongly recommended that the radio host monitor
the CTS pin to avoid this situation. The transceiver asserts this pin high as the buffer is filling
to signal the OEM Host to stop sending data. The transceiver will take CTS Low once the
buffer becomes less full.
Random Backoff Settings:
• 00h – Wait 1 packet time, then retry (Random Back Off is disabled)
• 01h – Wait 1 – 2 packet times, then retry
• 03h – Wait 1 – 4 packet times, then retry
• 07h – Wait 1 – 8 packet times, then retry
• 0Fh – Wait 1 – 16 packet times, then retry
• 1Fh – Wait 1 – 32 packet times, then retry
• 01h – Wait 1 – 2 packet times, then retry
• 03h – Wait 1 – 4 packet times, then retry
• 07h – Wait 1 – 8 packet times, then retry
• 0Fh – Wait 1 – 16 packet times, then retry
• 1Fh – Wait 1 – 32 packet times, then retry
• 3Fh – Wait 1 – 64 packet times, then retry
• 7Fh – Wait 1 – 128 packet times, then retry
• FFh – Wait 1 – 256 packet times, then retry
• 7Fh – Wait 1 – 128 packet times, then retry
• FFh – Wait 1 – 256 packet times, then retry
5.2.5
5.2.5
5.2.5
5.2.55.2.4
5.2.4
5.2.4
5.2.4
Duplex Mode
Duplex Mode
Duplex Mode
Duplex Mode
In Half Duplex mode, the AC4424 will send a packet out over the RF when it can. This can
cause packets sent at the same time by a Server and a Client to collide with each other over
the RF. To prevent this, Full Duplex Mode can be enabled. This mode restricts Clients to
transmitting on odd numbered frequency “bins” and the Server to transmitting on even
cause packets sent at the same time by a Server and a Client to collide with each other over
the RF. To prevent this, Full Duplex Mode can be enabled. This mode restricts Clients to
transmitting on odd numbered frequency “bins” and the Server to transmitting on even