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ARF169 Radio Modems - User guide version V1.4
3. Data exchange – Communication mode
Principe :
The communication mode is the default mode.
On switching on the modem is configured in RS232, 9.6kbps (serial link), 2.4kbps (RF data rate).
By default, the modem is in permanent listening mode of the RF interface and the UART port.
•
As soon as a frame from the RF link is demodulated, its content is transmitted to the UART port
•
As soon as a character chain is detected on the UART port, it is transmitted to the RF link.
"Air" communication takes place according to the following choice of protocols:
•
Packetized secured or non-secured
•
Continuous asynchronous (default mode)
3.1. Packet protocol
3.1.1 Protocol description
ARF169 modem uses a packet oriented protocol on its RF interface. The data coming from the UART interface are accumulated in an internal fifo
in the module and then encapsulated in an RF frame. The maximum amount of data that can be transferred into a single radio packet can reach
1024 Bytes.
The maximum packet size can be set up in S218 register from 1 to 1024 bytes. Each new packet introduces some latency in the transmission
delay caused by the RF protocol overhead. The RF protocols encapsulate the data payload with the following elements:
• A preamble pattern required for receiver startup time
• A bit synchronization pattern to synchronize the receiver on the RF frame
• Other protocol field such as source address and destination address, payload length, optional CRC and internal packet type field.
The incoming fifo may accumulate up to 1024 data byte. No more data has to be set in the fifo while a 1024 bytes block of data has not been
released by the radio transmission layer. To prevent from input fifo overrun, the hardware flow control may be activated. In this case, the RTS
signal will be set when the incoming fifo is almost full to prevent the host controller from sending new data.
3.1.2 Non-secured Packet Protocol
In non-secured mode, each packet is transmitted without acknowledgment; The transmitter doesn't know if packet has been received.
3.1.3 Secured Packet protocol
In secured mode, each packet is transmitted and acknowledged by the receiver. If a packet isn't acknowledged, the module proceeds with two
other attempts.
Following this sequence, the transmitter returns '>' if the packet has been received, or '#' if no acknowledgement has been received after the
three attempts.
Importante note : the addressed mode must be activated in order to use the secured mode.
3.1.4 Transmission integrity control
The RF protocol includes a 16 bits CRC. Each data extracted from an RF packet with an invalid CRC is silently discarded by the module state
machine. The CRC ensures that all the data received are valid. It may be deactivated for user whose protocols already have an integrity control
mechanism or when some error corrections are implemented by user protocols.
3.1.5 Implementation
The Packet protocol is selected by the S222 register.
•
Non-secured protocol : S222=0
•
Secured protocol : S222=2
3.1.6 Transmission data path
In packetized mode, the packet size is specified through register S218.
The modem starts the transmission of a complete packet when the number of data specified in S218 has been received.
If the number of data is inferior, an incomplete packet will be constituted when time out (specified in register S217) will be reached.
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