...some experiments with the ESP32 RMT generating DSHOT pulses for BLDC ESCs running BLHeli_S
The DSHOT protocol consists of transmitting 16-bit packets to the ESCs: 11-bit throttle value, 1-bit to request telemetry and a 4-bit checksum. There are three major protocol speeds: DSHOT150, DSHOT300 and DSHOT600.
| DSHOT | Bitrate | TH1 | TH0 | Bit Time µs | Frame Time µs |
|---|---|---|---|---|---|
| 150 | 150kbit/s | 5.00 | 2.50 | 6.67 | 106.72 |
| 300 | 300kbit/s | 2.50 | 1.25 | 3.33 | 53.28 |
| 600 | 600kbit/s | 1.25 | 0.625 | 1.67 | 26.72 |
| 1200 | 1200kbit/s | 0.625 | 0.313 | 0.83 | 13.28 |
The checksum is calculated over the throttle value and the telemetry bit, so the “first” 12 bits our value in the following example:
crc = (value ^ (value >> 4) ^ (value >> 8)) & 0x0F;
Biderictional DSHOT is also known as inverted DSHOT, because the signal level is inverted, so 1 is low and a 0 is high. This is done in order to let the ESC know, that we are operating in bidirectional mode and that it should be sending back eRPM telemetry packages.
The calculation of the checksum is basically the same, just before the last step the values are inverted:
crc = (~(value ^ (value >> 4) ^ (value >> 8))) & 0x0F;
References: