DESCRIPTION

The PCA II and PCA-3 are ISA (PC card) multichannel analyzers. The PCA Multiport is a standalone MCA that spec currently supports using GPIB. The PCA-3 and PCA Multiport both support counting to live-time and real-time presets and both return dead-time information. The PCA II only supports presets and dead-time corrections when used in conjunction with a CSS provided driver, which is only available on selected PC UNIX platforms. Otherwise, the PCA II can be used in user-level I/O mode, with the timing performed by some other hardware timer or the software clock.

The PCA-3 and PCA Multiport come with 16384 channels, while the PCA II only supports up to 8192 channels. When acquiring data, the channels can be partitioned into groups of 256, 512, 1024, ... channels up to a single group that contains all the channels. Thus, the PCA-3 and PCA Multiport allows a maximum of 64 groups of 256 channels, 32 groups of 512 channels, etc. The maximum number of groups on the PCA II depends on the amount of memory installed on the board.

DEVICE CONFIGURATION

MCA device configuration is entered on Aquisition device screen of the configuration editor along the following lines:

MCA (1D) and Image (2D) Acquisition Device Configuration

MCA            DEVICE   ADDR  <>MODE                             <>TYPE
 0  YES                0x1e0    POLL       The Nucleus PCA II MCA Board
 1  YES      /dev/pca  0x1e0    INTR       The Nucleus PCA II MCA Board
 2  YES                0x210                The Nucleus PCA-3 MCA Board
 3  YES                    7           The Nucleus PCA Multiport (GPIB)

Corresponding config file entries are of the sort:

PC_PCAII  =  anything  port_address  POLL  @mca_0

PC_PCAII  =  /dev/pca  port_address  INTR  @mca_1

PC_PCA3  =  port_address  @mca_2

GP_PCA_M  =  gpib_address  @mca_3

The first entry selects the PCA II in user-level polled mode. The second entry uses interrupt-driven mode which requires a kernel driver. See the drivers/README file in the spec distribution for information on installing the driver. The third entry is for the PCA-3 device. The fourth entry is for the GPIB PCA Multiport.

If using the interrupt-driven mode with the PCA II, note the following: Apparently, the PCA II doesn't trigger an interrupt on some PC mother boards. This problem can be fixed by changing the value of the resistor labeled R12 on the "PCA2 Memory Card" circuit diagram. This resistor is located near the lower left corner of the main board when viewed from the component side with the connector fingers pointing down and the input BNC to the right. R12 is about a centimeter down and to the left of the U26 IC. The circuit diagram indicates the resistor's value is 2K, however the boards seem to be shipped with a 1K resistor (brown-black-red stripes). Soldering a second 1K resistor alongside R12 and in parallel electrically will lower the resistance to 0.5K, which seems to work. (This modification was suggested by the manufacturer.)

FUNCTIONS

mca_get(arr) or mca_get(g, e)

Gets data from the currently selected MCA-type device, and transfers it to the array arr or to element e of data group g. Use of arrays rather than data groups is recommended. The native data type is ulong.

mca_par("disable", arg)

If arg is 1, prevents the PCA from being started and stopped by the standard counting functions tcount() and mcount(). If arg is 0, the PCA will be started and stopped with the standard counting functions (which is the default behavior).

mca_par("clear")

Clears the channels of the current group.

mca_par("run")

Programs the board with the current parameters and starts acquisition. For the PCA-3 and Multiport, acquisition time will be to the selected preset in real time or live time in PHA mode or the selected preset in number of passes in MCS mode. Note that the tcount() and mcount() functions, as used in the various counting macros, will also start PCA acquisition, however the PCA will free run until the count time passed to those functions has expired.

mca_par("halt")

Stops acquisition. Note that the PCA will also be halted when the tcount() and mcount() functions (as used in the various counting macros) complete their count intervals or are aborted.

mca_par("group_size")

Returns the current group size.

mca_par("group_size", size)

Sets the group size to size. Legal values are 256, 512, 1024, 2048, 4096, 8192 and 16384. On the PCA II, values above 1024 may not be legal if insufficient memory is installed on the board.

mca_par("select_group")

Returns the currently active group. Groups are numbered starting at zero.

mca_par("select_group", group)

Set the active group to group. The maximum number of groups equals the number of channels divided by the group size. If the group passed to the function is greater than the maximum number of groups, the current group selected is group modulus the maximum number of groups.

mca_par("pha")

Selects pulse-height analysis mode.

mca_par("gain")

Returns the current gain value used in pulse-height analysis mode.

mca_par("gain", value)

Sets the pulse-height analysis gain to value. Legal values are 256, 512, 1024, 2048, 4096 and 8192.

mca_par("offset")

Returns the current digital conversion offset used in pulse-height analysis mode.

mca_par("offset", value)

Sets the pulse-height analysis digital conversion offset to value. Legal values are multiples of 256 from 0 to 7936. An offset value shifts the channel contents.

mca_par("mcs")

Selects multichannel scaling mode.

mca_par("dwell")

Returns the current multichannel scaling dwell time.

mca_par("dwell", value)

Set the multichannel scaling dwell time. Allowed values are numbers between 1e-6 and 60 seconds with mantissa of 1, 2, 4 or 8. A value of -1 selects external dwell. If value isn't an allowed value, it is rounded to the nearest allowed value.

mca_par("mode")

Returns two if the PCA is in PHA live-time mode, one if the PCA is in PHA real-time mode and zero if the PCA is in MCS mode.

mca_par("readone", channel)

Returns the contents of channel number channel. The channel number is with respect to the current group.

mca_par("chan#")

Returns the contents of channel number #. The channel number is with respect to the current group.

mca_par("chan#", value)

Sets channel # to value. The channel number is with respect to the current group.

The following mca_par() functions are valid for the PCA-3 and PCA Multiport devices, but are only valid for the PCA II when the board is used with the interrupt-driven driver.

mca_par("preset")

In PHA mode, returns the current live-time or real-time preset value in seconds.

mca_par("preset", value)

In PHA mode, sets the current live-time or real-time preset value to value seconds. The PCA counts to the preset using mca_par("run"). When using mcount() or tcount() the PCA acquires until halted by spec.

mca_par("passes")

In MCS mode, returns the number of preset passes.

mca_par("passes", value)

In MCS mode, sets the number of passes to value. When using mcount() or tcount() the PCA acquires until halted by spec.

mca_par("live")

In PHA mode, selects live-time counting.

mca_par("real")

In PHA mode, selects real-time counting.

mca_par("dead")

In PHA mode, returns the percent dead time, if accumulating in live-time mode.

mca_par("elapsed_live")

In PHA live-time mode, returns the elapsed live time in seconds.

mca_par("elapsed_real")

In PHA mode, returns the elapsed real time in seconds.

mca_par("elapsed_passes")

In MCS mode, returns the elapsed number of passes.