![]() ![]() This triggers the U2 555 timer via U1a and starts a (R2 + R3)C3 ln(3) = 78.1µs = 9T conversion cycle, driving U1b to isolate the C2 hold capacitor (which holds the previous conversion result) and connect the C1 sample capacitor to the R1 input integration resistor. Serial transmission of bytes (at T = 8.68 µs = 115200 baud) for DA conversion follows standard UART formatting and begins with a ‘0’ start bit. ![]() Here’s how it works.įigure 2 The SDD with 5V asynchronous serial data, similar to a ♜ UART output.įigure 3 The SDD conversion cycle timing for 5V logic levels. UARTs are widely and inexpensively available, both as USB-driven external RS232 peripherals for PCs (typically using the popular FDTI or similar chipsets and available fully cabled and connectorized for less than $10) and as internal peripherals in popular microcontroller chips (the TM4C123x contains eight!).įigure 2 illustrates an SDD for 5-volt asynchronous serial data of the sort a ♜ UART might output, and Figure 3 is its timing diagram.Serializing and outputting binary numbers with LSB first is exactly what the standard universal asynchronous receiver/transmitter function (UART) does, and. ![]() Figure 1: The Shannon decoder DAC (SDD) concept.Īpplying the SDD concept to implementation of a DAC (or multiple DACs) benefits from some useful facts. ![]()
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