# LabJack write task

> Write command channel values to the analog and digital outputs of a LabJack.

A LabJack write task writes the values of command channels to the outputs of one LabJack device. For example, a valve on a schematic can switch `DIO4`, and a setpoint can drive `DAC0`.

Each output has a command channel and a [state channel](https://docs.synnaxlabs.com/reference/hardware/tasks#write-tasks). When you deploy the task, every output starts at 0. When you stop and start the task from the tasks toolbar or from code, the outputs go back to the last commanded values.

Before you start, you need a [configured device](https://docs.synnaxlabs.com/reference/hardware/labjack/configure-device).

## Create a LabJack write task

When you create command channels with a client library, give each one its own index channel. A writer that holds several commands on one index must write all of them in every frame.

[Enterprise](https://docs.synnaxlabs.com/reference/get-started/editions "Needs Synnax Enterprise")

**Console**

1. In the devices toolbar, right-click the device and select **Create write task**.
2. Set **State update rate**.
3. Click **Add channel**. In the port list of the channel, select **Analog** or **Digital**, then select the port.
4. Click (**Start**).

The Console creates the channels. For a device with the identifier `lj1`, the output `DIO4` gives the command channel `lj1_DIO4_cmd` with the index `lj1_DIO4_cmd_time`, and the state channel `lj1_DIO4_state` with the index `lj1_write_state_time`.

[](https://synnax.nyc3.cdn.digitaloceanspaces.com/docs/hardware/labjack/write-task-dark.mp4#t=0.001)

**Python**

Python does not create channels. Create them first.

```python
import synnax as sy
from synnax import labjack

dev = client.devices.retrieve(key="<serial number>")
state_time = client.channels.create(
    name="lj1_write_state_time", is_index=True, data_type=sy.DataType.TIMESTAMP
)
state = client.channels.create(
    name="lj1_DIO4_state", index=state_time.key, data_type=sy.DataType.UINT8
)
cmd_time = client.channels.create(
    name="lj1_DIO4_cmd_time", is_index=True, data_type=sy.DataType.TIMESTAMP
)
cmd = client.channels.create(
    name="lj1_DIO4_cmd", index=cmd_time.key, data_type=sy.DataType.UINT8
)

task = labjack.WriteTask(
    name="Valves",
    device=dev.key,
    channels=[
        labjack.DigitalWriteChannel(
            port="DIO4", cmd_channel=cmd.key, state_channel=state.key
        )
    ],
)
client.tasks.configure(task)
task.start()
```

Python creates the task on the embedded Driver of the Core. For a device on another Driver, use the Console or TypeScript.

**TypeScript**

TypeScript does not create channels. Create them first, as in the Python example.

```typescript
import { labjack } from "@synnaxlabs/client";

const dev = await client.devices.retrieve({ key: "<serial number>" });
const task = await client.tasks.create({
  name: "Valves",
  rack: dev.rack,
  type: "labjack_write",
  config: labjack.writeConfigZ.parse({
    device: dev.key,
    channels: [
      {
        type: "digital",
        port: "DIO4",
        cmdChannel: cmd.key,
        stateChannel: state.key,
      },
    ],
  }),
});
await task.start();
```

## Task options

| Console label     | Python field           | Default | Notes                                                                                |
| ----------------- | ---------------------- | ------- | ------------------------------------------------------------------------------------ |
| Device            | `device`               |         | The serial number of the device.                                                     |
| State update rate | `state_rate`           | 10 Hz   | How often the task writes the state channels.                                        |
| Data saving       | `data_saving_disabled` | On      | See [data saving](https://docs.synnaxlabs.com/reference/hardware/tasks#data-saving). |
|                   | `auto_start`           | Off     | Starts the task each time the Driver starts. Code only.                              |

## Channel reference

Each channel has a `cmd_channel` and a `state_channel`. Both are required.

**Analog**

#### [Analog](https://docs.synnaxlabs.com/reference/hardware/labjack/write-task#analog)

Python `AnalogWriteChannel`TypeScript `analog`

Outputs a voltage. The command is in volts, as `float32`.

| Setting | Default | Notes         |
| ------- | ------- | ------------- |
| `port`  | `DAC0`  | A `DAC` port. |

**Digital**

#### [Digital](https://docs.synnaxlabs.com/reference/hardware/labjack/write-task#digital)

Python `DigitalWriteChannel`TypeScript `digital`

Sets a digital line. The command is 0 or 1, as `uint8`.

| Setting | Default | Notes         |
| ------- | ------- | ------------- |
| `port`  | `DIO4`  | A `DIO` port. |

## Troubleshooting

* [output channels must set cmd_channel and state_channel](https://docs.synnaxlabs.com/reference/hardware/labjack/write-task#output-channels-must-set-cmd-channel-and-state-channel)

  * Cause

    A channel in code has no command channel or no state channel.

  * Fix

    Create both and set them on the channel.

For other problems, see [Configure a LabJack device](https://docs.synnaxlabs.com/reference/hardware/labjack/configure-device#troubleshooting) and [Troubleshoot hardware](https://docs.synnaxlabs.com/reference/hardware/troubleshooting).