(Computer Boards CIO-PCMDAS16 Cards – Snap-Master v3.20.3 and later)

In Software Burst Mode A/D Conversion, the sampling process for each analog channel consists of 5 steps:

1. Program the MUX
2. Program the Gain
3. Start the Conversion Sampling
4. Wait for EOC (End of Conversion)
5. Get Sample from the A/D Converter

With older, slower microprocessors, the time that elapsed between the end of step 5 for one channel and the start of step 3 for the next channel normally was sufficient for the MUX element to be properly recycled between channel samples.

With newer, faster microprocessors, the time between steps 5 and 3 can be so short that the MUX recycle process may not be completed between samples. A residual value from one channel may remain and interact with the new value of the following channel, resulting in “cross-channel bleed“, or “crosstalk“.

This effect is most likely to occur with Software or Hardware (IRQ) Pacing with a board having Software Burst Mode Sampling (e.g., in members of the CIO-PCMDAS16 families). If it occurs, the Delay Loop function allows the user to insert a controlled amount of delay between steps 2 and 3 of the sampling process, providing additional time for completion of the MUX recycle process.

The optimum value of delay magnitude is board and machine dependent. Since this delay reduces the benefit of burst-mode sampling, the user should experiment to find the minimum Delay Value in the Delay Loop Settings dialog which eliminates the crosstalk. In addition to needlessly increasing skew time, excessive delay at higher sample rates can interfere with basic channel sampling and operation of the board.

For boards or pacing modes not benefiting by this delay, the Delay Loop button will be absent or grayed out.