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NI PXIe-5122 will disabling one of the channels channel allow for more on board samples on the active channel.

I know there is a fixed on board memory size for each 5122, meaning dividing that number by 2 will be the available storage for each channel.  Will disabling one of the channels free up that memory for the other?  If not, what is the purpose of disabling/enabling channels?  Thanks

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Per the PXIe-5122 specifications, each channel has an allocated amount of memory for the buffer. That memory is listed as a "memory per channel" and should stay the same, even if you were to "disable" a channel.

 

Also, could you clarify what you mean by "disabling" a channel? I don't know of that being a function you can do on the PXIe card.

Christine B
Technical Support Engineer
National Instruments
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NISCOPE_ATTR_CHANNEL_ENABLED is a boolean attribute which can be controlled using the C driver calls.  It allows you to tell the scope whether to acquire data on a channel or not.  But if disabling a channel gives you no extra storage, what is the point?  You aren't going to be fetching from it anyway, why does it matter whether or not the scope itself has a notion of if you care about data from that channel.

http://zone.ni.com/reference/en-XX/help/370592AB-01/scopefunc/cviniscope_attr_channel_enabled/

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That attribute exists because for some scopes, you do have the ability to allocate extra "unused" memory to an active channel.

 

If you look at the PXI Oscilloscope offerings page, you can see that the spec for the "onboard oscilloscope memory size" for the 5122 is listed as MB/channel. For some of NI's newer cards, like the PXIe 5172, the onboard memory size is simply listed as "MB." When it's listed as "MB" instead of "MB/channel," the memory usually can be allocated differently depending on what channels are active. The PXIe-5172 specs (see Fig 😎 explain clearly how the number of enabled channels affects the allocated onboard memory per record. This offering is not listed on the 5122.

 

There are a couple different reasons that you might still want to disable a channel on the 5122, even if it doesn't increase the memory for the remaining channel:

1. When you call a "Fetch" function for the scope, you call from all active channels. Disabling a channel means you won't try to return info from the disabled channel.

2. If you want to ensure that another part of your program cannot access that channel, you can use the disable to prevent this.

Christine B
Technical Support Engineer
National Instruments
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