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KV Host Link Troubleshooting & Codes

This page summarizes common KEYENCE KV Host Link PLC errors for the PLC setup guide. It is not a complete manufacturer code table; use the KEYENCE manuals for formal definitions.

PLC Codes

Code Typical cause First check
E0 Device number is invalid, outside range, or not available on the selected PLC model. Check the address and selected canonical profile.
E1 Command is not supported by the selected PLC/model. Timer/counter preset writes are a common case on unsupported models. Check the model profile and avoid unsupported write helpers.
E2 Program is not registered. Check the PLC project/program state.
E4 Write is disabled by CPU protection, lock state, or project settings. Check KV Studio and CPU write-protection settings.
E5 Unit error. Check the PLC/unit error state.
E6 Comment data is not registered. Check comment registration before using comment reads.

Common Symptoms

Symptom Likely cause First check
The connection times out immediately. KV Host Link normally uses port 8501, not the SLMP/Computerlink example port 1025. Confirm the port in the library options or Node-RED connection node.
A timer or counter preset write returns E1. Host Link preset writes through WS / WSS are supported on KV-8000/7000-series, not on every KV model. Do not write timer/counter presets on unsupported models; use timer/counter read helpers for monitoring.
AT is rejected or missing on KV-X500. AT is not available in keyence:kv-x500 or keyence:kv-x500-xym. Check the selected profile before using AT.
X or Y is rejected or points look shifted. X and Y use decimal-bank plus hexadecimal-bit notation, for example X10F. Use the correct bank/bit notation and select an -xym profile when using XYM aliases.
R, MR, LR, or CR is rejected. These bit-bank families use two-digit bit notation rather than one plain hexadecimal number. Use forms such as R200:BIT or MR100:BIT.
DM100.D reads a bit instead of a 32-bit value. Dot notation means bit-in-word access; D after the dot is bit 13. Use the library's typed form such as DM100:D for unsigned 32-bit data.
DM100.3,4 or a similar bit-in-word count is rejected. Dot notation selects one bit inside one word and is scalar-only. Use DM100.3 for one bit, or use a direct bit family such as R200:BIT,4 for bit arrays.
A write to DM100:COMMENT is rejected. Device comments are read-only through the high-level Host Link helpers. Use :COMMENT only with read helpers.
Expansion unit buffer access fails. The selected unit number, buffer address, data format, or mounted module may not match the connected PLC hardware. Verify the expansion unit number and buffer address before using expansion buffer helpers.
CTH or CTC appears in a catalog but fails as an input address. CTH and CTC are catalog metadata rows for supported profiles. Treat them as catalog metadata only.
A non-canonical profile string is rejected. The profile catalog accepts exact canonical profile strings only. Copy the exact profile string from the profile list or setup guide.

First Checks

  • Confirm that Host Link / Upper Link communication is enabled on the PLC.
  • Confirm the port number, protocol, and IP settings in the KV PLC setup pages.
  • Confirm that the application selected the canonical profile for the actual PLC model.
  • For write errors, check CPU protection, lock state, project settings, and RUN-time write permission where applicable.