RF-LORA-868-SO (SX1272) Notes

The RF-LORA-868-SO module (from RF Solutions) looks to be an implementation of the Semtech reference design for the SX1272.

The SX1272 is very similar to the SX1276, but the register map is slightly different between the two. The following table was derived from source code for the Semtech LoraMac Node, specifically diffs of sx1272Regs-LoRa.h and sx1276Regs-LoRa.h. It serves as a side-by-side comparison when porting SX1276 code for use on an SX1272 chip, to save hunting back and forth between two datasheets.

Register SX1272 SX1276
AGCREF 0x43 0x61
AGCTHRESH1 0x44 0x62
AGCTHRESH2 0x45 0x63
AGCTHRESH3 0x46 0x64
PADAC 0x5A 0x4D
PLL 0x5C 0x70
PLLHOP 0x4B 0x44
TCXO 0x58 0x4B

The configuration of bits within some registers is also different. Most importantly, the modem configuration register bits have been juggled around a bit.

Register SX1272 SX1276
RegModemConfig1 (0x1d) Bw, Coding Rate, ImplicitHeaderOn, RxPayloadCrcOn, LowDataRateOptimize Bw, Coding Rate, ImplicitHeaderOn
RegModemConfig2 (0x1e) SpreadingFactor, TxContinuousMode, AgcAutoOn, SymbTimeout(9:8) SpreadingFactor, TxContinuousMode, RxPayloadCrcOn, SymbTimeout(9:8)

The RF switch used to select between RX and TX paths for the antenna is listed in the reference design as a Peregrine Semiconductor PE4259. The PE4259 datasheet states that it can be used in single-pin mode by tying !CTRL (pin 6) to Vdd, but the RF Solutions documentation states that two-pin mode must be used for the correct path to be selected. It might be worth investigating this (perhaps they use a different chip).

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