LoRa

1 Key Concepts

1.1 Spreading Factor

Note:

The Spreading Factor must be known in advance on both transmit and receive sides of the link as different spreading factors are orthogonal to each other

Spreading Factor 6:

Set Spreading Factor = 6 in Reg_ModemConfig2
The head must be set to Implicit mode
Set the DetectionOptimize of Reg_LoRaDetectOptimize to value '0b101'
Write 0x0C in the RegDetectionThreshold

void sx1278_set_spread_fact(uint8_t factor)
{
    uint8_t d;
    d = sx1278_read_reg(REG_MODEMCONFIG2);
    d = (d & MODEMCONFIG2_SF_MASK) | (factor << 4);
    sx1278_write_reg(REG_MODEMCONFIG2, d);

    if (factor == 6) {
        sx1278_write_reg(REG_DETECTIONOPTIMIZE, 0x5);                                       
        sx1278_write_reg(REG_DETECTIONTHRESHOLD, 0xC);                                      
    } else {
        sx1278_write_reg(REG_DETECTIONOPTIMIZE, 0x3);
        sx1278_write_reg(REG_DETECTIONTHRESHOLD, 0xA);                                      
    }
}

1.2 Signal Bandwidth

Note:

The Spreading Factor must be known in advance on both transmit and receive sides of the link

1.3 Coding Rate

2 TX

Static configuration registers can only be accessed in Sleep, Standby or FSTX mode
The LoRa FIFO can only be filled in Standby mode
Data TX is initiated by sending TX mode request
Upon completion the TxDone interrupt is issued and the radio returns to Standby mode
Following transmission the radio can be manually placed in Sleep mode or the FIFO refilled for subsequent TX operation

LoRa TX data FIFO filling:

Set Reg_FifoAddrPtr to Reg_FifoTxBaseAddr
Write PayloadLength bytes to the FIFO (Reg_Fifo)

Reg_Fifo 是 FIFO 的统一读写口，SPI 读写 Reg_Fifo，就会去 FIFO 内部地址为 Reg_FifoAddrPtr 的位置取放数据

TX_Modem 直接去 FIFO 地址为 Reg_FifoTxBaseAddr 的位置，取 PayloadLength 字节的数据

3 TX Power

1. Set Reg_PaConfig[7:7] to select PA output pin

0 to select RFO pin, Output power is limited to +14 dBm (25mW)
1 to select PA_BOOST pin, Output power is limited to +20 dBm (100mW)

2. Set Reg_PaConfig[6:4] to select max output power

Pmax = 10.8 + 0.6 * MaxPower [dBm], valide when user select the RFO pin as the output

3. Set Reg_PaConfig[3:0] to select OutputPower

Pout = Pmax - (15 - OutputPower) if PaSelect = 1 (RFO pin)
Pout = 17 - (15 - OutputPower) if PaSelect = 1 (PA_BOOST pin)

void sx1278_set_rf_maxpower()
{
    sx1278_write_reg(REG_PACONFIG, 0x8F);
}

LoRa

目录

1 Key Concepts

1.1 Spreading Factor

1.2 Signal Bandwidth

1.3 Coding Rate

2 TX

3 TX Power

4 Schematics

5 Chip

5.1 SX1278

6 Reference

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