# AT Commands User Guide

This document provides detailed usage instructions for the main AT commands supported by the H11 device.

## 1. AT+DEV_INIT_STA=GET

**Function**: Query device initialization status

**Command Format**:
```
AT+DEV_INIT_STA=GET
```

**Response Example**:
```
AT+DEV_INIT_STA=GET,4G,<4G_link>,<SIM_ready>,<NTRIP_flag>,<CSQ>,<data_back>,<upload_size>,<NTRIP_size>,GNSS,<status>,<reserved>,star,<SNR45>,<SNR48>,<SNR50>,<visible_stars>
OK
```

**Parameter Explanation**:
- `<4G_link>`: 4G network connection status (0=disconnected, 1=connected)
- `<SIM_ready>`: SIM card ready status (0=not ready, 1=ready)
- `<NTRIP_flag>`: NTRIP connection status (0=disconnected, 1=connected)
- `<CSQ>`: Signal quality (0-31, higher is better)
- `<data_back>`: Data upload status (0=idle, 1=uploading)
- `<upload_size>`: Upload queue size (bytes)
- `<NTRIP_size>`: NTRIP data queue size (bytes)
- `<status>`: GNSS module status
- `<SNR45>`, `<SNR48>`, `<SNR50>`: Number of satellites with SNR > 45/48/50 dB
- `<visible_stars>`: Total number of visible satellites

**Use Cases**:
- Check device module initialization status after startup
- Diagnose device connectivity and module status
- Monitor network and GNSS module status

---

## 2. AT+NEMATIME=SET

**Function**: Set NMEA output frequency

**Command Format**:
```
AT+NEMATIME=SET,<frequency>
```

**Parameters**:
- `<frequency>`: Output frequency in Hz (supported values: 1, 2, 5, 10)

**Response Example**:
```
AT+NEMATIME=SET
OK
```

**Error Response**:
```
AT+NEMATIME=SET
ERROR
```

**Use Cases**:
- Configure GNSS position data output rate
- Adjust positioning data update frequency based on application requirements
- Balance between update rate and power consumption

---

## 3. AT+NEMATIME=GET

**Function**: Query current NMEA output frequency

**Command Format**:
```
AT+NEMATIME=GET
```

**Response Example**:
```
AT+NEMATIME=GET,<frequency>
OK
```

**Parameter Explanation**:
- `<frequency>`: Current NMEA output frequency in Hz

**Use Cases**:
- Verify the current NMEA output frequency configuration
- Ensure frequency configuration has taken effect
- Troubleshoot positioning data update issues

---

## 4. AT+RTCMBASEPOS=GET

**Function**: Query base station position and distance from RTCM data source

**Command Format**:
```
AT+RTCMBASEPOS=GET
```

**Response Example** (when RTCM data is available):
```
AT+RTCMBASEPOS=GET,<latitude>,<longitude>,<altitude>,<distance>
OK
```

**Response Example** (when RTCM data is not available):
```
AT+RTCMBASEPOS=GET,0.0,0.0,0.0,0.0
OK
```

**Parameter Explanation**:
- `<latitude>`: Base station latitude in degrees (positive=North, negative=South)
- `<longitude>`: Base station longitude in degrees (positive=East, negative=West)
- `<altitude>`: Base station altitude/elevation in meters
- `<distance>`: Distance from device to base station in meters

**Use Cases**:
- Obtain current base station position information in RTK mode
- Monitor distance to reference station
- Assess differential positioning quality
- Verify RTK connection status

---

## Command Usage Examples

### Query device initialization status
```
→ AT+DEV_INIT_STA=GET
← AT+DEV_INIT_STA=GET,4G,1,1,1,25,0,0,1024,GNSS,1,0,star,8,5,2,12
← OK
```

### Set NMEA frequency to 1Hz
```
→ AT+NEMATIME=SET,1
← AT+NEMATIME=SET
← OK
```

### Query current NMEA frequency
```
→ AT+NEMATIME=GET
← AT+NEMATIME=GET,1
← OK
```

### Query base station position and distance
```
→ AT+RTCMBASEPOS=GET
← AT+RTCMBASEPOS=GET,31.135370,121.287729,22.467,1234.56
← OK
```

---

## Important Notes

1. **Command Format**: All AT commands start with "AT" and end with "\r\n"
2. **Case Insensitive**: Commands are case-insensitive
3. **Response Timeout**: Recommended timeout for each command is 5 seconds
4. **Response Format**: Successful execution returns "OK", failure returns "ERROR"
5. **RTCM Base Station Info**: Base station position is only available after receiving valid RTCM 1005/1006 messages
6. **Frequency Setting**: Device may need restart for frequency changes to take effect
7. **Line Ending**: Use CR+LF (\r\n) as line terminator
8. **Serial Parameters**: Default baud rate is 115200 bps

---

## Related Information

- **NMEA**: National Marine Electronics Association protocol, widely used in GPS/GNSS devices
- **RTCM**: Radio Technical Commission for Maritime Services, data format for differential positioning
- **RTK**: Real-Time Kinematic positioning technology
- **CSQ**: Signal Quality indicator (0-31, where 31 is excellent)
- **SNR**: Signal-to-Noise Ratio measured in dB