# Variables for Reading and Writing Channels in a Real-Time Sequence

Use parameter and channel reference variables to read or write system definition channels.

There are key differences between how parameters and channel references access channels. Use the following table to determine the best variable type to read or write channels in your real-time sequence.
Variable Use case Limitations
Parameter Use parameters to create real-time sequences that you can use across multiple system definition files. Parameters are difficult to manage if a stimulus profile contains nested real-time sequences or real-time sequences that access many channels.
Channel Reference Use channel references if you do not need to use a real-time sequence with multiple system definition files. In general, channel references are easier to manage than parameters. Channel references bind a real-time sequence to a specific system definition file.

To illustrate how channel references are easier to manager than parameters, consider a real-time sequence, SeqA, that calls another sequence, SeqB. The stimulus profile, MyProfile, manages both sequences. You need to read a channel, named MyChannel, from SeqB.

The following illustration contrasts how reading MyChannel with a channel reference differs from reading MyChannel with a parameter.
Parameters Channel Reference
• Add a parameter and assign MyChannel to it.
• Add the parameter to the real-time sequence code.
• Add a channel reference for MyChannel.
• Add the channel reference to the real-time sequence code to read or write the system definition channel.
Note

You do not need to configure the channel reference in SeqA or MyProfile.

• Add a parameter and assign it to MyChannel.
• Call SeqB and declare the MyChannel parameter in the real-time sequence call.
• Configure the parameter assignments so that the appropriate SeqA parameter is assigned to MyChannel.