Binary Packets & Bandwidth

For IMU600-V2 / firmware 0.11.2 / GUI v1.6.1.

Use MODE,binary for UART1 binary output. Commands remain ASCII; ACK / NAK / INFO replies use 0x7F TEXT frames. UART2 defaults to binary. Units and status / flags match ASCII.

Frame & CRC

D6 44 | id (1) | len (1) | seq (1) | payload (len) | crc16 (2)
Field Rule
sync 0xD6 0x44
id / len Message ID / payload length 0–255 bytes
seq Independent per ID and UART, wrapping 8-bit counter
payload Little-endian; f32 = IEEE-754 single precision
crc16 CRC-16/CCITT-FALSE: poly 0x1021, init 0xFFFF, no reflection, xorout 0; covers id / len / seq / payload; CRC stored LE 
def crc16_ccitt(data: bytes) -> int:
    crc = 0xFFFF
    for byte in data:
        crc ^= byte << 8
        for _ in range(8):
            crc = ((crc << 1) ^ 0x1021) & 0xFFFF if crc & 0x8000 else (crc << 1) & 0xFFFF
    return crc

assert crc16_ccitt(b"123456789") == 0x29B1

def frame_crc_ok(frame: bytes) -> bool:
    if len(frame) < 7 or frame[:2] != b"\xd6\x44":
        return False
    size = frame[3]
    return (len(frame) == size + 7 and
            crc16_ccitt(frame[2:5 + size]) ==
            int.from_bytes(frame[5 + size:7 + size], "little"))

Message Table

ID Name Payload bytes Python struct
0x01 IMU_RAW 68 <BBHQ3f3ff3f3ff
0x02 IMU (fused) 68 <Q3f3ff3f3ffBBBB
0x03 BARO 24 <QfffB3x
0x04 AHRS 52 <Q4f3f3fBBH
0x05 PPS 24 <QIIiBBH
0x10 STAT 44 <BBBB9IHH
0x11 FUS 32 <6Iff
0x12 SYS 48 <7IHBBBBBBIII
0x7F TEXT Variable ASCII string without $ or *XX

Payload Field Order

0x01 IMU_RAW:
imu_id:u8, status:u8, n:u16, ts_us:u64,
gyro[3]:f32, acc[3]:f32, temp:f32, dth[3]:f32, dv[3]:f32, dt:f32

0x02 IMU:
ts_us:u64, gyro[3]:f32, acc[3]:f32, temp:f32,
dth[3]:f32, dv[3]:f32, dt:f32,
n_used:u8, flags:u8, used_mask:u8, reserved:u8

0x03 BARO:
ts_us:u64, press_hpa:f32, temp_c:f32, alt_m:f32, status:u8, reserved[3]:u8

0x04 AHRS:
ts_us:u64, q[4]:f32, roll:f32, pitch:f32, yaw:f32,
gyro_bias[3]:f32, align:u8, flags:u8, zb_ds:u16

0x05 PPS:
ts_us:u64, edges:u32, captures:u32, err_ppb:i32, state:u8, align:u8, age_ms:u16

0x10 STAT:
imu_id:u8, dry_timeout:u8, dry_pin:u8, isr_cpu_pct:u8,
dry:u32, out:u32, crc_err:u32, frame_err:u32, spi_timeout:u32,
dropped:u32, dcnt_skip:u32, dry_kicks:u32, resync:u32,
isr_us_max:u16, isr_us_last:u16

0x11 FUS:
outputs:u32, rej[3]:u32, incomplete:u32, degraded:u32,
gyro_thresh:f32, acc_thresh:f32

0x12 SYS:
uart_drop:u32, loops_per_s:u32, uart_resets:u32, pps_cnt:u32,
baro_samples:u32, baro_i2c_err:u32, baro_timeouts:u32,
rate_hz:u16, isr_cpu_total_pct:u8, out_mode:u8, baro_stale:u8,
baro_hz:u8, proto_mode:u8, pps_state:u8, u2_drop:u32, trig_cnt:u32, trig_rej:u32
  • Binary AHRS places quaternion before Euler angles, unlike ASCII. zb_ds uses 0.1 s; ASCII zb_s uses seconds.
  • Binary PPS uses err_ppb, ASCII err_ppm; positive means the local clock is faster.
  • used_mask bit n means IMU n+1 was used. SYS out_mode: 0 none / 1 raw / 2 fused / 3 both; proto_mode: 0 ascii / 1 binary. Parse SYS by len: 48 bytes for this version, 40 for fw 0.8.0, or 36 for older firmware.

Bandwidth Planning

8N1 uses 10 bits per byte, so 460800 bps provides about 46 kB/s. These binary estimates come from the manual; allow margin for commands and statistics. ASCII generally needs about twice the bandwidth.

Configuration Approx. Traffic Baud Requirement
50 Hz both + AHRS + BARO 19 kB/s 460800
100 Hz both + AHRS + BARO 37 kB/s 460800
200 Hz fused + AHRS 27 kB/s 460800
400 Hz fused + AHRS 54 kB/s 921600
500 Hz fused + AHRS 67 kB/s 921600
1000 Hz one RAW IMU (sizing reference) 75 kB/s 921600
1000 Hz fused + AHRS 134 kB/s 1500000 / 2000000

raw actually sends all three IMUs, not just one: at 1000 Hz it needs about 225 kB/s, exceeding the roughly 200 kB/s ceiling at 2000000 bps. Select fused or reduce RATE. Full UART buffers discard whole lines/frames; monitor uart_drop / u2_drop. UART loss does not by itself imply SPI loss.

Payload Byte Offsets

Offsets below start at payload byte 0, excluding the five sync / id / len / seq bytes. Total UART frame length is payload + 7. These are also distinct from whole-packet SPI offsets.

0x01 IMU_RAW · 68 / 75 bytes

Offset Field Type
0 imu_id u8
1 status u8
2 n u16
4 ts_us u64
12 gyro[3] f32 ×3
24 acc[3] f32 ×3
36 temp f32
40 dth[3] f32 ×3
52 dv[3] f32 ×3
64 dt f32

0x02 IMU · 68 / 75 bytes

Offset Field Type
0 ts_us u64
8 gyro[3] f32 ×3
20 acc[3] f32 ×3
32 temp f32
36 dth[3] f32 ×3
48 dv[3] f32 ×3
60 dt f32
64 n_used u8
65 flags u8
66 used_mask u8
67 reserved u8

0x03 BARO · 24 / 31 bytes

Offset Field Type
0 ts_us u64
8 press_hpa f32
12 temp_c f32
16 alt_m f32
20 status u8
21 reserved[3] u8 ×3

0x04 AHRS · 52 / 59 bytes

Offset Field Type
0 ts_us u64
8 q[4] f32 ×4
24 roll / pitch / yaw f32 ×3
36 gyro_bias[3] f32 ×3
48 align u8
49 flags u8
50 zb_ds u16

0x05 PPS · 24 / 31 bytes

Offset Field Type
0 ts_us u64
8 edges u32
12 captures u32
16 err_ppb i32
20 state u8
21 align u8
22 age_ms u16

0x10 STAT · 44 / 51 bytes

Offset Field Type
0 imu_id u8
1 dry_timeout u8
2 dry_pin u8
3 isr_cpu_pct u8
4 dry u32
8 out u32
12 crc_err u32
16 frame_err u32
20 spi_timeout u32
24 dropped u32
28 dcnt_skip u32
32 dry_kicks u32
36 resync u32
40 isr_us_max u16
42 isr_us_last u16

0x11 FUS · 32 / 39 bytes

Offset Field Type
0 outputs u32
4 rej[3] u32 ×3
16 incomplete u32
20 degraded u32
24 gyro_thresh f32
28 acc_thresh f32

0x12 SYS · 48 / 55 bytes

Offset Field Type
0 uart_drop u32
4 loops_per_s u32
8 uart_resets u32
12 pps_cnt u32
16 baro_samples u32
20 baro_i2c_err u32
24 baro_timeouts u32
28 rate_hz u16
30 isr_cpu_total_pct u8
31 out_mode u8
32 baro_stale u8
33 baro_hz u8
34 proto_mode u8
35 pps_state u8
36 u2_drop u32
40 trig_cnt u32
44 trig_rej u32

The two lengths in each heading are payload / complete frame. For legacy 36 / 40-byte SYS, read only present trailing fields. STAT read_retry / read_bad exist only in ASCII. PPS age_ms saturates at 65535 and align=1 means PPS-aligned output. AHRS zb_ds uses 0.1 s and was zero before fw 0.9.2.

0x7F TEXT contains the ASCII body without $, *XX or CRLF, for example SPNVACK,RATE,100; maximum complete frame length is 262 bytes. ACK / NAK and textual BOOT / RESET / DBG / AUTH / INIT / HB / STALL / TRAP messages use this type.

Communication details also follow Protocol v1.1, pages 21–26. See the protocol overview.

Source document：IMU600-V2 User Manual v1.1 · PDF pages 25–28

Read Source Pages · Document Crosswalk and Differences

Category overview · All setup guides