SX1276IMLTRT View Datasheet(PDF) - Semtech Corporation

Part Name

Description

Manufacturer

SX1276IMLTRT

137 MHz to 1020 MHz Low Power Long Range Transceiver

Semtech Corporation 

SX1276/77/78/79

WIRELESS, SENSING & TIMING

DATASHEET

The LoRa receive modem can work in two distinct mode

1. Single receive mode

2. 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 period of time. If a preamble hasn’t been found at the end

of the time window, the chip generates the RxTimeout interrupt and goes back to Standby mode. The length of the

reception 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.

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 Standby mode.

The modem will also automatically return in Standby mode when the interrupts RxDone is 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 FifoAddrPtr to FifoRxBaseAddr.

2 Static configuration register device can be written in either Sleep mode, Standby 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 Standby 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 (FifoAddrPtr) to the base location in memory

(FifoRxBaseAddr).

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 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 (measured in

symbol periods) the preamble will be dropped and the search for a preamble restarted. However, this scenario will not be

flagged by any interrupt. In continuous RX mode, opposite to the single RX mode, the RxTimeout interrupt will never occur

and the device will never go in Standby mode automatically.

It is also important to note that the demodulated bytes are written in the data buffer memory in the order received. Meaning,

the first byte of a new packet is written just after the last byte of the preceding packet. The RX modem address pointer is

never reset as long as this mode is enabled. It is therefore necessary for the companion microcontroller to handle the

address pointer to make sure the FIFO data buffer is never full.

Rev. 4 - March 2015

©2015 Semtech Corporation

Page 40

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