Getting started

Start here

Use this page to make your first KEYENCE KV Host Link connection from Rust. The examples select the canonical profile keyence:kv-7000, use the high-level async API, and read from DM0 before any write.

Prerequisites

Requirement	Value
Rust	Stable Rust compatible with this crate.
Async runtime	tokio with macros and rt-multi-thread enabled for #[tokio::main].
PLC host	192.168.250.100
PLC port	8501
Protocol	KEYENCE KV Host Link Upper Link over TCP.

Add dependency

cargo add plc-comm-hostlink-rust

The package name is plc-comm-hostlink-rust; the import path in Rust code is plc_comm_hostlink.

Choose profile

Use the exact canonical profile string that matches your PLC model when you need the device range catalog. The library does not infer the catalog from the PLC model response.

use plc_comm_hostlink::device_range_catalog_for_plc_profile;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let catalog = device_range_catalog_for_plc_profile("keyence:kv-7000")?;
    println!("{}", catalog.plc_profile);
    Ok(())
}

Connect

HostLinkConnectionOptions::new("192.168.250.100") uses TCP port 8501 by default.

use plc_comm_hostlink::{HostLinkClient, HostLinkConnectionOptions};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let options = HostLinkConnectionOptions::new("192.168.250.100");
    let client = HostLinkClient::connect(options).await?;

    println!("{:?}", client.is_open().await);

    client.close().await?;
    Ok(())
}

First read

Start with a DM read because it is the simplest word-register path on most KV setups.

use plc_comm_hostlink::{HostLinkClient, HostLinkConnectionOptions};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client =
        HostLinkClient::connect(HostLinkConnectionOptions::new("192.168.250.100")).await?;

    let dm0 = client.read_typed("DM0", "U").await?;
    println!("{:?}", dm0);

    client.close().await?;
    Ok(())
}

Expected output shape:

U16(1234)

The numeric value depends on your PLC state.

First write

Use a dedicated test address only. The example uses DM120 because the existing validation notes reserve nearby DM addresses for smoke checks on one test setup; choose an address that is safe on your PLC program.

use plc_comm_hostlink::{HostLinkClient, HostLinkConnectionOptions};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client =
        HostLinkClient::connect(HostLinkConnectionOptions::new("192.168.250.100")).await?;

    client.write_typed("DM120", "U", 1234_u16).await?;
    let dm120 = client.read_typed("DM120", "U").await?;
    println!("{:?}", dm120);

    client.close().await?;
    Ok(())
}

Confirm success

1. Confirm your PLC is reachable at 192.168.250.100:8501.
2. Confirm the connection example prints true.
3. Confirm the first read prints a HostLinkValue, such as U16(...).
4. Confirm any write uses a test-only DM address.
5. Restore the test register if your procedure requires a known value.

If it does not work

Symptom	Check
Connection fails immediately	The default port is 8501, not 1025.
Profile selection fails	Use one of the exact strings in PROFILES.md; aliases and old combined names are rejected.
You need the verification binary	Build it with cargo build --features cli --bin hostlink_verify_client.
Reads fail on special devices	Start with DM reads first, then move to timers, counters, aliases, or comments.

Detailed edge cases live in GOTCHAS.md.

Next pages

Page	Link
Usage guide	USAGE_GUIDE.md
PLC profiles	PROFILES.md
Supported registers	SUPPORTED_REGISTERS.md
Gotchas	GOTCHAS.md