Getting started

Start here

This page gets you from an empty .NET project to your first KEYENCE KV Host Link read. You will connect to your PLC at 192.168.250.100:8501, read DM0, then write and restore a test register.

Prerequisites

Requirement	Value
.NET SDK	.NET 8, 9, or 10 SDK for consuming the package; the .NET 10 SDK is required to build or run this repository's samples.
PLC network	Your KV PLC must be reachable from your PC.
Host Link port	Use port 8501 for TCP or UDP unless your PLC connection node is configured differently.

Install

dotnet add package PlcComm.KvHostLink

Connect

using PlcComm.KvHostLink;

var options = new KvHostLinkConnectionOptions("192.168.250.100", 8501, HostLinkTransportMode.Tcp, "keyence:kv-8000");
await using var client = await KvHostLinkClientFactory.OpenAndConnectAsync(options);

This opens the ordinary client, which is the recommended surface for normal application code. It includes arrival-order FIFO admission; no queued wrapper is needed. The port, TCP/UDP transport, and canonical PLC profile are all explicit. The factory performs the network connection; constructing options does not. Host Link endpoints are IPv4-only. An IPv6 literal and a bracketed IPv4 literal such as [192.168.250.100] are rejected before socket creation. Write IPv4 addresses without brackets; a hostname must resolve to IPv4.

First read (step by step)

using System;
using PlcComm.KvHostLink;

var options = new KvHostLinkConnectionOptions("192.168.250.100", 8501, HostLinkTransportMode.Tcp, "keyence:kv-8000");
await using var client = await KvHostLinkClientFactory.OpenAndConnectAsync(options);

ushort dm0 = (ushort)await client.ReadTypedAsync("DM0", "U");
Console.WriteLine($"DM0 = {dm0}");

Expected output:

DM0 = 123

Your number will match the current value stored in DM0 on your PLC.

First write

These controlled-test examples restore only confirmed writes, in reverse order. An outcome-unknown write stops further writes and propagates its original error; inspect and reconcile the PLC state before proceeding. A readback failure after a confirmed write still attempts restoration. A restoration failure is reported and stops the remaining restoration steps.

using System;
using PlcComm.KvHostLink;

var options = new KvHostLinkConnectionOptions("192.168.250.100", 8501, HostLinkTransportMode.Tcp, "keyence:kv-8000");
await using var client = await KvHostLinkClientFactory.OpenAndConnectAsync(options);

const string testAddress = "DM100";
ushort original = (ushort)await client.ReadTypedAsync(testAddress, "U");
ushort testValue = (ushort)Random.Shared.Next(0, ushort.MaxValue + 1);

bool write1Confirmed = false;
bool outcomeUnknown1 = false;
try
{
    await client.WriteTypedAsync(testAddress, "U", testValue);
    write1Confirmed = true;
    ushort readback = (ushort)await client.ReadTypedAsync(testAddress, "U");
    Console.WriteLine($"{testAddress} = {readback}");
}
catch (HostLinkOutcomeUnknownError)
{
    outcomeUnknown1 = true;
    throw;
}
finally
{
    if (!outcomeUnknown1)
    {
        if (write1Confirmed)
        {
            await client.WriteTypedAsync(testAddress, "U", original);
        }
    }
}

Only write to a test address that is safe for your machine and program.

Confirm success

1. The connection opens without a timeout.
2. The first read prints a value for DM0.
3. The write example prints the value written to DM100.
4. After a confirmed write, the finally block attempts to restore the original test-register value; check any restoration error.

If it does not work

Symptom	Check
The connection fails immediately.	Confirm that the explicitly configured port and TCP/UDP transport match the PLC connection settings.
An IPv6 endpoint is rejected.	Use the PLC's IPv4 address or a hostname with an IPv4 result. IPv6 is intentionally unsupported.
A bracketed IPv4 endpoint is rejected.	Remove the brackets: use 192.168.250.100, not [192.168.250.100].
A command reports HostLinkNotConnectedError.	Call OpenAsync after construction or after a timeout, cancellation, close, EOF, or transport failure.
A read reports HostLinkTimeoutError.	The one transaction deadline expired and invalidated the connection. Check the endpoint and timeout, then explicitly call OpenAsync before another command.
A write reports HostLinkOutcomeUnknownError.	Transmission may have begun, but no definitive result was received. Inspect Reason, do not retry automatically, determine PLC state safely, then explicitly reopen if appropriate.
Reads fail while you are trying the first example.	Start with DM word reads; do not start with timer/counter or expansion buffer access.
Timer/counter preset writes return E1.	Timer/Counter preset writes (WS/WSS) are only supported on KV-8000/7000-series.

This library

Source	plc-comm-hostlink-dotnet
Package	NuGet: PlcComm.KvHostLink
Changelog	CHANGELOG.md
Report a problem	Issues