Communications Calculators
11 free calculators with formulas and worked examples.
UART baud rate, I2C pull-up, SPI timing, CAN bus, USB termination, RS-485, I2S, LIN bus, Modbus frame timing, and Ethernet cable calculators.
UART Baud Rate
Calculate UART frame timing, throughput, and USART BRR register divisor from baud rate, data format, and MCU clock frequency. Identify baud rate error for reliable serial communication.
I2C Pull-Up
Calculate I2C pull-up resistor values for Standard (100 kHz), Fast (400 kHz), and Fast-Plus (1 MHz) modes. Derives minimum, maximum, and recommended resistance from supply voltage and bus capacitance per NXP UM10204.
Clock Jitter
Calculate clock tree timing budget for FPGA and SoC designs. Enter reference oscillator jitter, PLL noise floor, buffer stages, and target clock frequency to compute setup margin.
SPI Timing
Calculate SPI bus timing parameters including bit period, frame time, maximum clock frequency limited by trace capacitance, and signal slew rate
CAN Bus Timing
Calculate CAN bus bit timing parameters including prescaler, time quanta, sync segment, propagation segment, and phase buffer segments for a given baud rate and sample point
USB Termination
Calculate USB bus termination resistor values, differential impedance, cable propagation delay, signal rise time, and eye opening for USB 2.0 and USB 3.0
RS-485 Termination
Calculate RS-485 bus termination resistors, bias resistors, maximum baud rate for cable length, propagation delay, and bias current consumption
I2S Timing
Calculate I2S bit clock (BCLK), word clock (LRCLK/WCLK), and data rate for audio interfaces at any sample rate, bit depth, and channel count.
LIN Bus Timing
Calculate LIN bus bit time, break field length, frame time, and maximum frame rate for automotive LIN network design.
Modbus Timing
Calculate Modbus RTU character time, 3.5-character inter-frame gap, total frame duration, and maximum frame rate.
Ethernet Cable
Calculate Ethernet cable attenuation, maximum cable length, and pass/fail for Cat5e, Cat6, Cat6a, and Cat8 at 100Mbps, 1Gbps, and 10Gbps.
About Communications Calculators
Digital communication protocols define the electrical signaling, timing, framing, and error-detection mechanisms that allow ICs to exchange data reliably. Most embedded systems use several protocols simultaneously: SPI for high-speed peripheral access, I2C for low-pin-count sensor buses, UART for debug and host communication, CAN for automotive/industrial control, and USB for host interfaces.
UART (universal asynchronous receiver-transmitter) is the simplest: each byte is framed with a start bit, data bits, optional parity, and stop bit(s). Baud rate must match on both ends within ±2-3% or bit-framing errors occur. The baud rate calculator computes the prescaler value for common MCU clock frequencies and warns about achievable accuracy.
I2C uses two wires (SCL, SDA) with open-drain signaling — pull-up resistors set the rise time, which must be fast enough for reliable sampling but slow enough to avoid ringing. Pull-up value depends on bus capacitance, supply voltage, and maximum operating frequency (100 kHz standard, 400 kHz fast, 1 MHz fast+). Undersized pull-ups cause signal integrity failures; oversized ones waste current.
SPI has no formal timing standard — each device datasheet specifies setup and hold times relative to the clock edge. The SPI timing calculator verifies that a given clock frequency satisfies setup/hold margins across the signal chain including PCB trace delays. CAN bus timing involves segment lengths (sync, prop, phase1, phase2) that together determine bit timing and sample point position — critical for multi-node networks spanning automotive harnesses.