NI digital read task

Read the digital input lines of an NI device into channels.

An NI digital read task reads the digital input lines of one NI device into channels. Each line gives 0 or 1. For example, it can record limit switches on port0/line0 and port0/line1 of a USB-6343.

Before you start, you need a configured device.

Ports and lines

NI devices group digital lines into ports. Each channel reads one line, set by its port and line numbers. The device manual lists the ports and lines.

The Driver reads the lines on the computer clock, at the Sample rate. See timing.

The Console gives the digital read tasks of a device one index channel, and only one writer can hold an index channel. So only one of these tasks can run on a device at a time, even when the tasks use different lines. A second task stops right after it starts, with an error that names the running task. Tasks from a client library have this limit only when they share an index channel.

Create an NI digital read task

In the devices toolbar, right-click the device and select Create digital read task.
Set Sample rate and Stream rate.
Click Add channel, then enter the port and the line in Port/Line.
Click (Start).

The Console creates the channels. For a device with the identifier dev1, port 0, line 1 gives dev1_di_0_1, with the index channel dev1_di_time.

Python does not create channels. Create them first.

import synnax as sy
from synnax import ni

dev = client.devices.retrieve(key="<device key>")
time = client.channels.create(
    name="dev1_di_time", is_index=True, data_type=sy.DataType.TIMESTAMP
)
limit = client.channels.create(
    name="limit_switch", index=time.key, data_type=sy.DataType.UINT8
)

task = ni.DigitalReadTask(
    name="Limit switches",
    device=dev.key,
    sample_rate=100,
    stream_rate=10,
    channels=[ni.DIChannel(port=0, line=1, channel=limit.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 does not create channels. Create them first.

import { ni } from "@synnaxlabs/client";

const dev = await client.devices.retrieve({ key: "<device key>" });
const time = await client.channels.create({
  name: "dev1_di_time",
  isIndex: true,
  dataType: "timestamp",
});
const limit = await client.channels.create({
  name: "limit_switch",
  index: time.key,
  dataType: "uint8",
});

const task = await client.tasks.create({
  name: "Limit switches",
  rack: dev.rack,
  type: "ni_digital_read",
  config: ni.digitalReadConfigZ.parse({
    device: dev.key,
    sampleRate: 100,
    streamRate: 10,
    channels: [{ port: 0, line: 1, channel: limit.key }],
  }),
});
await task.start();

Task options

Console label	Python field	Default	Notes
Device	`device`		The key of the device.
Sample rate	`sample_rate`	10 Hz	Up to 1,000,000 Hz in the Console.
Stream rate	`stream_rate`	5 Hz	Up to 20,000 Hz. See read tasks.
Data saving	`data_saving_disabled`	On	See data saving.
Auto start	`auto_start`	Off	Starts the task each time the Driver starts.

Channel reference

Each channel has a channel, the Synnax channel that records the value as uint8. The table shows the Console label of each setting, with its Python field under it.

Setting	Default	Notes
Port/Line `port`, `line`	`0`/`0`	The port, and the line in it.

Troubleshooting

Port ..., line ... has already been used on another channel
Cause
Two channels use the same line.
Fix
Change the port or the line of one of them.
... has no control authority - it is currently held by ...
Cause
Another running task writes to the same index channel. The error names that task.
Fix
Stop the other task, or move its channels into this task.

For other problems, see Configure an NI device and Troubleshoot hardware.

Counter read task

Digital write task