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RFM95 Datasheet(PDF) 35 Page - HOPE Microelectronics CO., Ltd.
HOPE [HOPE Microelectronics CO., Ltd.]
Tel: + 86-755-82973805
Fax: + 86-755-82973550
E-mail: firstname.lastname@example.org http:/ / www.hoperf.com
The LORA receive modem can work in two distinct mode
Single receive mode
Continuous receive mode
Those two modes correspond to different use cases and it is important to understand the subtle differences between them.
Single Reception Operating Mode
In this mode, the modem searches for a preamble during a given time window. If a preamble hasnāt been found at the end
of the time window, the chip generates the RxTimeout interrupt and goes back to stand-by mode . The length of the window
(in symbols) is defined by the RegSymbTimeout register and should be in the range of 4 (minimum time for the modem to
acquire lock on a preamble) up to 1023 symbols. (The default value being 5). If no preamble is detected during this window
the RxTimeout interrupt is generated and the radio goes back to stand-by mode.
At the end of the payload, the RxDone interrupt is generated together with the interrupt PayloadCrcError if the payload
CRC is not valid. However, even when the CRC is not valid, the data are written in the FIFO data buffer for post processing.
Following the RxDone interrupt the radio goes to stand-by mode.
The modem will also automatically return in stand-by mode when the interrupts RxDone or RxTimeout are generated.
Therefore, this mode should only be used when the time window of arrival of the packet is known . In other cases, the RX
continuous mode should be used.
In Rx single mode low-power is achieved by turning off PLL and RF blocks as soon as a packet has been received. The
flow is as follows:
1 Set FifoPtrAddr to FifoRxPtrBase.
2 Static configuration register device can be written in either Sleep mode, Stand-by mode or FSRX mode.
3 A single packet receive operation is initiated by selecting the operating mode RXSINGLE.
4 The receiver will then await the reception of a valid preamble. Once received, the gain of the receive chain is set.
Following the ensuing reception of a valid header, indicated by the ValidHeader interrupt in explicit mode. The packet
reception process commences. Once the reception process is complete the RxDone interrupt is set. The radio then returns
automatically to Stand-by mode to reduce power consumption.
5 The receiver status register PayloadCrcError should be checked for packet payload integrity.
6 If a valid packet payload has been received then the FIFO should be read (See Payload Data Extraction below). Should
a subsequent single packet reception need to be triggered, then the RXSINGLE operating mode must be re-selected to
launch the receive process again - taking care to reset the SPI pointer (FifoPtrAddr) to the base location in memory
Continuous Reception Operating Mode
In continuous receive mode the modem scans the channel continuously for a preamble. Each time a preamble is detected
the modem detects and tracks it until the packet is received and then carries on waiting for the next preamble.
If the preamble length exceeds the anticipated value set by the registers
RegPreambleMsb and RegPreambleLsb
symbol unit), the preamble will be dropped and the search for a preamble restarted. However, this scenario will not be
flagged by an interrupt. In continous RX mode, opposite to the single RX mode, when a timeout interrupt is generated, the
device will not go in standby mode. In this case, the user must simply clear the interrupt while the device carry on waiting
for a valid preamble.
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