New-Tech Europe Magazine | June 2019

Microcontroller based UARTs Many microcontrollers, such as the Microchip Technology PIC16F688T-I/ SL, include serial data interfaces for communicating with monitors, external analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), or other microcontrollers (Figure 4). The EUSART, sometimes called a serial communications interface (SCI), can be configured as either a full-duplex asynchronous or a half- duplex synchronous serial data link. The EUSART in the PIC16F688T-I/SL contains all of the shift registers, clock generators, and data buffers necessary to perform an input or output serial data transfer independent of microcontroller program execution. It has a two-character receive buffer and a single-character transmit buffer. The full-duplex asynchronous interface is useful for communicating with external peripherals like a display monitor, which is the primary application for this interface in the microcontroller. Line drivers Line drivers augment the operation of UARTs by buffering the transmit and receive signals. They are useful because they operate over the full RS- 232 voltage level specification. One example of such a device is the Texas Instruments MAX232DR dual RS-232/ TIA/EIA-232-F transceiver (Figure 5). The MAX232DR line driver/receiver has advantages in industrial applications where higher voltages are required. It can sustain input voltages of up to ±30 volts. The device includes a capacitive voltage generator using four external capacitors to supply RS-232 voltage levels of -5 to -7 volts and +5 to +7 volts at the outputs from a single 5 volt supply. Differential signaling RS-232 uses single-ended connections for the transmit and receive line. With

Figure 4: The Microchip Technology PIC16F688T-I/SL CMOS microcontroller includes a serial interface using an enhanced universal synchronous/asynchronous receiver/transmitter (EUSART). (Image source: Microchip Technology)

Figure 5: Applying the MAX232DR dual driver/receiver to buffer a TL16C752D dual UART. The MAX232DR can tolerate input voltages up to ±30 volts, while outputs are protected against shorts to ground. (Image source: Texas Instruments)

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