In the Configuration, Data Rates 0 to 4 should be used (DR_0 to DR_4). Data Rates 8 to 13 (DR_8 to DR_13) are being used only for downlinks (downstream, gateway to node) and should not be used in the configuration . Only DR_0, DR_1, DR_2, DR_3, DR_4 should be used for US configuration.
So if you use DR_0 (SF10 125kHz) for an uplink , it will automatically use DR_0 + 8 = DR_8 for downlink (SF12 500kHz). Likewise, if you use DR_1 for uplink it will use DR_9 for downlink. (SF10 is maximum SF for uplinks, SF12 for downlinks)
Furthermore, you can select channels on which these are sent and received. Each channel can handle all datarates (DR_0, DR_1, DR_2 and DR_3), except DR_4 which uses special channels. For LoRaWAN US region, a total of 64 uplink channels plus 8 downlink channels are possible where:
- Sub-band 1 represents uplink channels 0-7 + downlink channel 0;
- Sub-band 2 represents uplink channels 8-15 + downlink channel 1;
- Sub-band 3 represents uplink channels 16-23 + downlink channel 2;
- Sub-band 4 represents uplink channels 24-31 + downlink channel 3;
- Sub-band 5 represents uplink channels 32-39 + downlink channel 4;
- Sub-band 6 represents uplink channels 40-47 + downlink channel 5;
- Sub-band 7 represents uplink channels 48-55 + downlink channel 6;
- Sub-band 8 represents uplink channels 56-63 + downlink channel 7;
- Sub-band ALL represents all channels
Upstream – 64 channels numbered 0 to 63 utilizing LoRa 125 kHz BW varying from DR0 to DR3 , using coding rate 4/5, starting at 902.3 MHz and incrementing linearly by 200 kHz to 914.9 MHz
Upstream – 8 channels numbered 64 to 71 utilizing LoRa 500 kHz BW at DR4(only) starting at 903.0 MHz and incrementing linearly by 1.6 MHz to 914.2 MHz
Downstream – 8 channels numbered 0 to 7 utilizing LoRa 500 kHz BW at DR8 to DR13 , starting at 923.3 MHz and incrementing linearly by 600 kHz to 927.5 MHz
Source: https://lora-alliance.org/resource-hub/lorawanr-regional-parameters-v103reva page 21 to 27