UARTQuickGuidebsicsnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn

UARTQuickGuidebsicsnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn

• 1.
  UART (Universal Asynchronous Receiver/Transmitter) Quickreference: concepts, wiring, configuration, and debugging
• 2.
  What is UART? •Point to point serial interface on many ‑ ‑ MCUs/SoCs • Asynchronous: no separate clock; both ends agree on timing (baud rate) • Typical uses – debug console, GPS, Bluetooth modules (HC 05), ‑ sensors, modems • Full duplex on two wires: TX and RX (+ GND)
• 3.
  Signal Levels • TTL/CMOSlogic – 0–3.3 V or 0–5 V (MCU pins), idle HIGH • RS 232 ‑ – ±3…±12 V, inverted logic, needs level shifter (MAX3232) • RS 485/422 ‑ – Differential pair for long distance / multi drop ‑
• 4.
  Frame Format • Startbit (LOW) • 5–9 data bits (LSB first) • Optional parity: None/Even/Odd • 1–2 stop bits (HIGH) • Common shorthand: 8 N 1, 7 E 1, etc. ‑ ‑ ‑ ‑
• 5.
  UART Frame (Example:8 N 1) ‑ ‑ Idle (High) Star t D0 D1 D2 D3 D4 D5 D6 D7 Pari ty Sto p Line idle = HIGH. Start bit pulls line LOW, then LSB first data bits, optional parity, and ‑ one or more STOP bits (HIGH).
• 6.
  Key Parameters • Baudrate – bits per second, e.g., 9600/115200 • Word length – 5..9 bits • Parity – None / Even / Odd • Stop bits – 1 / 1.5 / 2 • Flow control – None / RTS CTS (hardware) / XON XOFF (software) ‑ ‑
• 7.
  Baud Rate Generation •Most UARTs oversample (×16) and use a divider • Generic formula: USARTDIV = f_clk / (16 × baud) • Example @ 72 MHz, 115200 bps → USARTDIV ≈ 39.0625 • Program integer & fractional parts per MCU (e.g., STM32 BRR)
• 8.
  Wiring Basics • CrossTX↔RX – MCU_TX → Module_RX, MCU_RX ← Module_TX • Share ground • Optional – RTS/CTS lines for hardware flow control • Level shifting – Use MAX3232 for RS 232; logic level shifters for ‑ ‑ 5 V↔3.3 V
• 9.
  Common Errors • Baudmismatch → garbled text • Wrong polarity/levels (RS 232 vs TTL) ‑ • No common ground • Frame/Parity/Overrun errors when ISR/DMA too slow
• 10.
  Registers (Typical) • DATA –TX register / RX register (read to clear) • STATUS – TXE (empty), TC (complete), RXNE (data), ORE/FE/PE (errors) • CTRL – enable TX/RX, parity, stop bits, interrupts, DMA
• 11.
  Pseudocode: Init // Configurebaud = 115200 for a 72 MHz clock (example MCU) enable_clock(UART1); gpio_set_mode(TX_PIN, ALT_PUSH_PULL); gpio_set_mode(RX_PIN, INPUT_FLOATING); UART1.BRR = calc_brr(F_CLK=72e6, BAUD=115200); // divider UART1.CR1 = UART_ENABLE | TX_ENABLE | RX_ENABLE; UART1.CR1 |= RXNEIE; // enable RX interrupt (optional) // or enable DMA for TX/RX
• 12.
  Pseudocode: TX/RX (polling) voiduart_write(char c){ while(!(UART1.SR & TXE)); // wait until TX register empty UART1.DR = (uint8_t)c; } int uart_read(void){ if(UART1.SR & RXNE) return (int)(UART1.DR & 0xFF); return -1; // no data } // Example uart_write('H'); uart_write('i'); uart_write('n'); int ch = uart_read(); // returns -1 if no byte available
• 13.
  Interrupt/DMA • RX interruptfor low latency byte capture ‑ • DMA for high throughput with ring buffers • Use timeouts or delimiters to frame packets
• 14.
  Simple Packet Design •Add header (e.g., 0x55), length, payload, checksum/CRC • Escape special bytes or use SLIP/COBS framing • Validate checksum before processing
• 15.
  RS 485 Notes(Multi drop) ‑ ‑ • Half duplex on differential pair A/B ‑ • Transceiver DE/RE pin to switch TX/RX • 120 Ω termination at both ends; bias resistors to define idle state • Use addressing in your packet format
• 16.
  Debugging Tips • Startat 9600 8 N 1; echo characters to verify ‑ ‑ link • Use a USB UART dongle + terminal ‑ (PuTTY/minicom) • Check with logic analyzer/oscilloscope • Print status flags when things go wrong
• 17.
  Checklist • Right voltage& level shifting • TX↔RX crossed and GND common • Baud/format match both ends • Flow control consistent (None vs RTS/CTS) • Use robust framing & checksums for binary data