MT3333 All-in-One GNSS
Figure 5-2: Power on/off reset behavior
5.11. Serial interfaces
MT3333 supports three serial interfaces: UART, SPI and I2C. The active serial interface type is determined by strap
pins. Note that firmware with SPI and I2C support is available on request, the standard chipset firmware supports
5.11.1. Universal Asynchronous Receiver/Transmitter (UART)
MT3333 has three full duplex serial ports that can be used for serial data communication. UART communication
functions provided include: UART data transmission/receive and NMEA sentences input/output. In general, UART0
is used for NMEA output and PMTK command input, while UART1 is RTCM input. You can adjust the UART2 port as
desired. UART provides signal or message outputs.
5.11.2. Serial Peripheral Interface (SPI)
Note: SPI support is available in firmware on request.
The SPI port manages the communication between digital baseband (BB) and external devices. MT3333 supports
both master and slave modes. In the master mode only 4 bytes of register can be transferred. In slave mode 4-
byte-register or SRAM FIFO options are available. In the SRAM FIFO mode, the size of the data blocks transmitted
and received is 256 bytes. The clock phase and clock polarity are selectable. MT3333 supports a manual or
automatic indicator for data transfer in the slave mode.
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