ADS, Beckhoff's Automation Device Specification, in pure Elixir, as a client: reading, writing and watching the variables of a TwinCAT PLC by name, over TCP or over Secure ADS (TLS).

• ADS.Client talks to a PLC, or any other ADS device, over one connection, with many requests on the way at once, and reconnects by itself.
• ADS.Discovery finds PLCs on the network, and adds and deletes routes on them, over UDP; ADS.Client.routes/2 lists them, and mix ads.route does all three from the command line; mix ads.info shows a system's state, host name and network adapters.
• ADS.Codepage is the code page of the PLC's strings, Windows-1252 unless told otherwise.
• ADS.Type turns PLC values into Elixir terms and back, from the types the PLC describes or ones given by hand.
• ADS.Symbol and ADS.DataType are the PLC's own descriptions of its variables and types.
• ADS.AMS, ADS.Command and ADS.Sum encode and decode, for those who bring their own transport; ADS.Secure and ADS.Certificate are for Secure ADS.

Addresses

An ADS device is reached by the AMS NetId of the system it runs on, six numbers such as "5.36.69.176.1.1", and its AMS port on that system:

A NetId has nothing to do with an IP address, though it's often made from one by adding .1.1. Inside a device, data is addressed by an index group and an index offset, both 32 bits, or by the name of a variable, such as "MAIN.nCounter".

States

A device is in one of the ADS states, an atom here: :invalid, :idle, :reset, :init, :start, :run, :stop, :save_config, :load_config, :power_failure, :power_good, :error, :shutdown, :suspend, :resume, :config and :reconfig; or the number of a state that has no name.

Errors

• {:error, name}: the device or a router answered with an ADS return code, such as :device_symbol_not_found (see ADS.ReturnCode), or its number if it has no name
• {:error, :timeout}: no answer in time
• {:error, :closed}: there's no connection, or it was lost before the answer came
• {:error, {:invalid_response, data}}: the answer doesn't fit the request

A request that doesn't fit the protocol, or a value that doesn't fit its type, raises ArgumentError in the caller and is never sent.