// LEARN

Host Link Guide

A step-by-step introduction to Host Link, the protocol that lets a PC read and write KEYENCE KV series PLCs — starting from the command format. Useful whether you use a library or implement it yourself.

  1. 01 What is Host Link? How a PC talks to a KEYENCE KV series PLC Host Link is the communication function that lets a PC or other external device read and write the devices of a KEYENCE KV series PLC. This article covers port 8501, the ASCII commands, TCP vs UDP and the available commands, based on the KEYENCE manual.
  2. 02 Host Link command and response format (RD, RDS, WR, WRS) How to write KEYENCE KV series Host Link commands and read their responses, walked through with real examples. Covers the separating spaces, device notation, the digits of the .U, .S, .D, .L and .H data formats, timer/counter reads and 32-bit values.
  3. 03 Host Link error responses E0–E6: meaning and fixes What the error responses a KEYENCE KV series PLC returns over Host Link (E0, E1, E2, E4, E5, E6) mean and what usually causes them, based on the manual and on tests with real hardware.
  4. 04 Host Link devices and point limits (KV-8000 / 7000 / 5000 / Nano) The devices and number ranges you can specify over KEYENCE KV series Host Link, the number of points RDS and WRS can read or write at once, and the limits for monitor registration and continuous force set, by model.
  5. 05 Host Link by hand vs. KcpX vs. KV COM+ Library in C# The same task — reading DM100–DM102 from a KEYENCE KV series PLC — written three ways: sending Host Link commands yourself, the .NET library KcpX, and KEYENCE's KV COM+ Library. We compare code size, setup, supported environments and when each one fits.