NARROW BAND - NB868 - User guide version V2.2.5 - Software version V2.3.0
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three attempts.
Importante note
: the addressed mode must be activated in order to use the secured mode.
3.2.1.4
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.
3.2.1.5
Implementation
The Packet protocol is selected by the S222 register.
•
Non-secured protocol : S222=0
•
Secured protocol : S222=2
3.2.1.6
Transmission data path
In packetized mode, the packet size is specified through register S218.
The module 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.
3.2.2 Continuous asynchronous protocol
3.2.2.1
Description of the protocol
The continuous asynchronous protocol enables data transfer from the UART interface to the radio link with the lowest possible latency. It is
associated with radio modulations enabling a wide range of air data rate and ranges to be covered. This is the mode that will allow you to use
the NB868 module to the maximum of its possibilities.
• In transmission, data entering on the UART is immediately transmitted into the “air”.
•
In reception, data from the RF frames is transmitted progressively to the UART interface.
There is no buffering of complete radio frames before or after transmission on the serial link.
However, the product has buffering enabling a buffer to be performed if the radio and UART data rates are different. The UART interface does
not require a specific protocol. Each octet transmitted is transferred into the air and vice versa.
Thanks to its low latency and the absence of a protocol on the UART port, the NB868 module used with the continuous asynchronous protocol
is completely transparent in the replacement of a wire link.
3.2.2.2
Transmission integrity control
By definition, the continuous protocol can not be cut. There is therefore neither CRC calculation nor control of data integrity.
3.2.2.3
Implementation
The continuous asynchronous protocol is selected by the S222 register.
It can use the following radio data rates: 2.4kbps, 9.6kbps, 38.4kbps and 57.6kbps. The adjustment of the radio data rate is done via the S254
register.
The notions of addressing (broadcast communication, group communication and addressed communication between products) are available and
described below.
3.2.2.4
Transmission data path and latency
Transmission delay from one equipment to another will depend on different factor:
• The UART transmission rate of the transmitter
• The UART transmission rate of the receiver
• The radio transmission rate and the radio modulation used
• The radio protocol overhead (packet split, preamble, synchronization and other protocol fields)
• The input data fifo threshold and timeout
