SCEA065B November   2018  – March 2021 SN74AVC4T774 , SN74AXC1T45 , SN74AXC4T245 , SN74AXC4T774 , SN74AXC8T245 , SN74AXC8T245-Q1 , SN74AXCH1T45 , SN74AXCH4T245 , SN74AXCH8T245


  1.   Trademarks
  2. 1Introduction
  3. 2Common Interfaces and AXC Implementation
    1. 2.1 General Purpose Input Output (GPIO)
    2. 2.2 Serial Peripheral Interface (SPI)
      1. 2.2.1 Voltage Translation for SPI
      2. 2.2.2 SPI Applications
    3.     8
    4. 2.3 UART
      1. 2.3.1 Voltage Translation With UART
      2. 2.3.2 UART Applications
    5. 2.4 Joint Test Action Group (JTAG)
      1. 2.4.1 JTAG Applications
    6. 2.5 Reduced Gigabit Media Independent Interface (RGMII)
      1. 2.5.1 Voltage Translation for RGMII
      2. 2.5.2 RGMII Applications
      3. 2.5.3 Skew Performance
  4. 3Summary
  5. 4Related Documentation
  6. 5Revision History


Universal Asynchronous Receiver/Transmitter (UART) is a hardware device that enables two or four signal, asynchronous, full duplex communication interfaces. The UART is responsible for converting parallel data to serial for transmission, and vice-versa for receiving. In the two signal UART variation, the signals are host transmit (TX) and host receive (RX). In the four signal variation, there are RX and TX signals, as well as ready-to-send (RTS) and clear-to-send (CTS), which are used for handshaking. The data frame consists of a low level start bit, data bits, optional parity bit, and the stop bits. While the UART does handle data framing, generating, and receiving data, it does not define a common signaling method between devices. The UART output is a signal at the operating voltage of the device, such as 1.2 V or 2.5 V. These signals are acceptable for use in short distances between two UARTs operating at the same voltage level. Since this is not usually the case, the signal from the UART is usually sent to a line driver to convert the signal to a standard such as RS-232 or RS-485. The standards allow longer distance communication through defined signal characteristics. RS-232 uses a voltage range of –12 V to 12 V to improve noise margin on the line. RS-485 uses differential pairs to transmit a signal. Both RS-485 and RS-232 standards use UART data framing, yet a transceiver is necessary to invert and translate the UART signals. Since UART is asynchronous, there is no clock signal. Instead, both communicating devices must be configured to use the baud rate, equivalent to bits per second (bps) in UART. UART is generally considered a low speed interface with speeds between 300 bps to 115 kbps.