Linx EVM-900-PRO, Руководство по данным

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Carrier Sense Multiple Access (CSMA)
CSMA is an optional feature. It is a best-effort delivery system that listens
to the channel before transmitting a message. If CSMA is enabled and
the module detects another transmitter on the same channel, it waits until
the active transmitter finishes before sending its payload. This helps to
eliminate RF message corruption and make channel use more efficient.
When a module has data ready to transmit and CSMA is enabled, it listens
on the intended transmit channel for activity. If no signal is detected,
transmission is started.
If a carrier is detected with an RSSI above the CSMA threshold in the
CRSSI register, transmission is inhibited. If a signal below the threshold is
detected that has a compatible preamble or packet structure, transmission
is also inhibited.
If the module is synchronized from a recent packet transfer, it waits for a
random interval, then checks again for activity. If the detected carrier lasts
longer than the time allowed for the current channel, the module hops to
the next channel in the hop sequence and again waits for a clear channel
before transmitting.
If the module is not synchronized, it hops to the next channel and again
checks for interference. When no activity is detected it starts transmitting.
Using the Command Response (CRESP) Line
The CRESP line is high when sending data bytes and low when
sending command response bytes. This indicates to an external host
microcontroller that the data on the CMD_DATA_OUT line is a response
to a command and not data received over-the-air. CRESP is held in the
correct state at least one byte time after the last byte for the indicated
source (command response or data, although it normally stays in the same
state until a change is required).
If a data packet is received when the module is processing a command, it
sends the command response, raises CRESP, and then sends the received
data bytes.
When reading or writing the module’s register settings, it is possible for
incoming RF data to intermix with the module’s response to a configuration
command. This can make it difficult to determine if commands were
successfully processed as well as to capture the received RF data. Setting
the CMDHOLD register to 0x01 causes the module to store incoming
RF traffic (up to the RF buffer capacity) while the CMD line is low. When
the CMD line is returned high, the module outputs the buffered data on
the UART. This allows the external host microcontroller to have separate
configuration times and data times instead of potentially having to handle
both at once.
The CRESP line stays low for at least ten bit times after the stop bit of the
last command response. Figure 28 shows the timing.
CMD_DATA_OUT
CRESP
D0 ... D6 D7
10 bit
times
Stop Start
Figure 28: HumPRO-A
TM
Series Transceiver CRESP Line Timing