When to use: Use this when laying out a Modbus RTU, PROFIBUS, or other RS-485 multidrop serial network to verify the segment respects the TIA/EIA-485-A limits. A standard segment supports up to 32 unit loads and the maximum cable length trades off against baud rate (≈ 4000 ft / 1200 m at ≤ 100 kbps, derating at higher speeds). Both ends must be terminated with 120 Ω resistors matching the cable characteristic impedance, and stubs/drops kept short to avoid reflections.