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Using Computer Boards PCMCIA Cards with Snap-Master

There have been a number of questions regarding the setup and use of Computer Boards PCMCIA data acquisition cards. This application note covers three areas: Installation, Calibration, and the Delay Loop setting.

Installation

Many of the new computers on the market, especially Pentium type computers, use a newer PCMCIA controller on the computer’s motherboard. For these machines, Winbook XP5s in particular, you must follow the following steps in order to get the PCMCIA boards to work.

NOTE: You must be able to acquire data using the CBTEST DOS utility before the cards will work in MS-Windows 3.1 and Windows 95 with Snap-Master.

  • Gather all the driver and utility software that came with your computer, and the CIO PCM cards. Make sure that you have the latest INSTACAL software (check out www.computerboards.com).
  • Install and configure the Card and Socket services which came with your computer. Contact your computer manufacturer you do not have them, or if you suspect that the ones you do have are out dated. You must use the ones that came with your computer in order to assure that they were designed for your particular PCMCIA controller.
  • Install the latest ComputerBoards, Inc. INSTACAL program along with the current CBCLIENT software supplied by ComputerBoards, Inc., and the RTPL program supplied by ComputerBoards, Inc.
  • Make sure that the CBCLIENT.COM is located in the directory defined by the CBDIREC environment variable, or to a directory that is on the path.
  • Add CBCLIENT to AUTOEXEC.BAT if it is not already there.
  • Reboot
  • Insert the ComputerBoards PCM card (it will probably not be recognized). If it is not recognized, it will probably give a low pitched tone when you plug it in. If it is recognized, it may give off a higher pitched beep.
  • Run the RTPL.EXE program supplied by ComputerBoards, Inc. Insert and remove PCM card to reconfigure it. It should now be recognized.
  • It will probably be necessary to run a utility that is specific to the Card & Socket Services in use to define the card more completely. These utilities are different from each vendor, but the information required is generally the same.
  • At this point you should be able to setup the card using the INSTACAL program. If you have problems loading INSTACAL, use the CDCAL and CBTEST utilities directly supplying a command line argument of the board you want to configure after the command. For example, to run on logical board 0, type “cbtest 0″ followed by a carriage return.
  • Once you have entered the INSTACAL program you should configure your particular PCMCIA card using the install menu option. Configure the base address and interrupt level in this menu. Write down these settings so you know them when you set up Snap-Master.
  • Once you have set up the board using the install menu, move on to the Test menu, and select your board. Follow the on-screen instructions for testing the board using the Plot menu option. You should see data coming in from the A/D card at this point. If you do not see data at this point, please contact ComputerBoards for further assistance.
  • Once you are getting data in this screen, you can move on to setting up Snap-Master in Windows. Make sure you include the Computer Boards hardware driver when installing Snap-Master. The Base Address and IRQ settings made under INSTACAL must be inserted in the appropriate places in the Configuration window of the Snap-Master instrument.

Calibration

Snap-Master uses a slightly different calibration routine than the one found in INSTACAL. If you calibrate the hardware using only INSTACAL, Snap-Master will probably report slightly different voltages than what is being input to the A/D.

Here is an overview of the steps performed by the Calibration routine in Snap-Master for each available input range (gain):

  • Set the A/D to read the internal reference voltage of 0V on channel 0 (offset calculation).
  • Read 100 consecutive values from the A/D and calculate the average.
  • Set the A/D to read the internal reference voltage of 30% of full scale (gain calculation).
  • Read 100 consecutive values from the A/D and calculate the average.
  • Calculate the Gain Adjustment Factor from the gain and offset averages of the +/- 5V (for bipolar) or 0-5V (for unipolar) readings
  • Calculate the Offset Adjustment Factor based on the Gain calculated above and the offset reading for the input range

The resulting gain and offset values are stored in the configuration file (CBI2.CNF) used by Snap-Master. Because each board is different, you should perform the calibration in Snap-Master each time you insert a PCMCIA card in the computer.

Delay Loop

There are 5 distinct steps to acquiring data from an A/D:

1. Program the MUX
2. Program the Gain
3. Start the conversion sampling
4. Wait for EOC (End of Conversion)
5. Read the 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 is absent or grayed out.