The L86-M33 is a GNSS receiver module, developed by Quectel, that is only capable of receiving signals from the GPS and GLONASS constellation. Some GNSS receivers can receive signals from additional constellations, such as Galileo and BeiDou.
/* GNSS Receiver: Quectel L86-M33 (library) */
/* Filename: L86-M33.h */
/* Communication Protocol: UART */
/* Author: Michael */
void PMTK_CMD_FULL_COLD_START(void) // Factory settings (NMEA 0183 standard command)
{
while (U1STAbits.UTXBF == 1); // Wait for transmit buffer to be empty of at least one character
U1TXREG = '$';
while (U1STAbits.UTXBF == 1);
U1TXREG = 'P';
while (U1STAbits.UTXBF == 1);
U1TXREG = 'M';
while (U1STAbits.UTXBF == 1);
U1TXREG = 'T';
while (U1STAbits.UTXBF == 1);
U1TXREG = 'K';
while (U1STAbits.UTXBF == 1);
U1TXREG = '1';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = '4';
while (U1STAbits.UTXBF == 1);
U1TXREG = '*';
while (U1STAbits.UTXBF == 1);
U1TXREG = '3';
while (U1STAbits.UTXBF == 1);
U1TXREG = '7';
while (U1STAbits.UTXBF == 1);
U1TXREG = 13; // Carriage return to return cursor to beginning of current line
while (U1STAbits.UTXBF == 1);
U1TXREG = 10; // Cursor moves to next line
}
void PMTK_API_SET_NMEA_OUTPUT(void) // Output RMC only (NMEA 0183 standard command)
{
while (U1STAbits.UTXBF == 1);
U1TXREG = '$';
while (U1STAbits.UTXBF == 1);
U1TXREG = 'P';
while (U1STAbits.UTXBF == 1);
U1TXREG = 'M';
while (U1STAbits.UTXBF == 1);
U1TXREG = 'T';
while (U1STAbits.UTXBF == 1);
U1TXREG = 'K';
while (U1STAbits.UTXBF == 1);
U1TXREG = '3';
while (U1STAbits.UTXBF == 1);
U1TXREG = '1';
while (U1STAbits.UTXBF == 1);
U1TXREG = '4';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '1';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = ',';
while (U1STAbits.UTXBF == 1);
U1TXREG = '0';
while (U1STAbits.UTXBF == 1);
U1TXREG = '*';
while (U1STAbits.UTXBF == 1);
U1TXREG = '2';
while (U1STAbits.UTXBF == 1);
U1TXREG = '9';
while (U1STAbits.UTXBF == 1);
U1TXREG = 13;
while (U1STAbits.UTXBF == 1);
U1TXREG = 10;
}The following list describes how each of the functions in the L86-M33.h library work:
- PMTK_CMD_FULL_COLD_START, line #6, sets the L86-M33 to factory settings.
- PMTK_API_SET_NMEA_OUTPUT, line #38, sets the L86-M33 to display basic navigation data.
The PMTK NMEA Packet Protocol is a command standard, developed by MediaTek, used to configure a GNSS receiver, as shown in Table 1.
| Field | Bytes | Description | Example | ||
| $ | 1 | Preamble | $ | ||
| Talker ID | 1 | P | P | ||
| NMEA Data Type | 3 | MTK | MTK | ||
| Data Field | Packet Type | 3 | 000 to 999 | 314 | |
| Packet Data | var. | ( , ) delimited | ,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 | ||
| * | 1 | End of data field | * | ||
| Checksum | 2 | Hexadecimal number calculated by XOR of all characters between “$” and “*” | 29 | ||
| <CR><LF> | 2 | End of packet | <CR><LF> | ||
An example of a PMTK command is shown, i.e., $PMTK314,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0*29<CR><LF>, which instructs a GNSS receiver to produce sentences with a RMC interval (Recommended Minimum Specific GNSS Sentence). The checksum, 29, can be calculated using a checksum calculator and copy-pasting in “PMTK314,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0”.
Quectel uses a Software Development Kit (SDK) in developing commands specific to the L86-M33 GNSS receiver, as shown in Table 2.
| Field | Bytes | Description | Example | |
| $ | 1 | Preamble | $ | |
| Talker ID | 2 | PQ | PQ | |
| Packet Type | 1 – 10 | Instruct decoder how to decode packet | BAUD | |
| Data Field | var. | ( , ) delimited | ,W,9600 | |
| * | 1 | End of data field | * | |
| Checksum | 2 | Hexadecimal number calculated by XOR of all characters between “$” and “*” | 4B | |
| <CR><LF> | 2 | End of packet | <CR><LF> | |
An example of a SDK command is shown, i.e., $PQBAUD,W,9600*4B, which instructs the L8-M33 GNSS receiver to produce sentences at a rate of 9600bps. Note that a “W”/”R” character in the Data Field represents a write/read command, respectively.