|
NAME DAC - Digital-To-Analog (DAC) Motors
DESCRIPTION
spec has built-in C code to treat a number
of digital-to-analog converter (DAC) devices as motors. The
standard commands for moving motors and reading motor positions
will set and get corresponding values on the DAC registers. The
"move" of a DAC motor is instantaneous - the value
corresponding to the target position is written at once to the
DAC register.
The DAC hardware supported includes ISA boards with either
byte or word access, PCI boards with word access, VME modules
with an A16 addressing mode and USB devices. (The configuration
described here is not used for the CAMAC DSP E250, KS 3112/6 and
KS 3195 DAC modules, which can also be used as DAC motors.)
Digital I/O, which is an independent hardware feature often
included with the DAC devices, is supported using
motor_par() commands as described below.
DEVICE CONFIGURATION
Each DAC module should be configured on the Devices screen of
the configuration editor. Currently supported DAC controller
types are:
|
-
DAC as motor (ISA - byte access)
DAC as motor (ISA - word access)
DAC as motor (VME A16 addressing)
DAC as motor (PCI)
DAC as motor (USB)
|
|
For the byte-access mode for ISA cards, spec
first writes the high-order byte to one plus the register
address, then writes the low-order byte to the register address.
The specific PCI DAC cards currently supported are the
Measurement Computing models PCI-DDA02/12, PCI-DDA04/12, PCI-
DDA08/12, PCI-DDA02/16, PCI-DDA04/16, PCI-DDA08/16, PCI-DAC6702
and PCI-DAC6703.
On the USB bus, the Measurement Computing USB-3100 series
models are supported. These devices all use 16-bit DACs.
The Acromag model 921x VME modules are specifically detected.
For those modules, spec adds 0x80 to the base
address and left shifts 12-bit values as required by these
modules. Other VME modules that support DAC registers using A16
addressing may also work with the existing support.
Recognition for other PCI boards, USB devices and VME modules
will be added in response to user requests.
MOTOR CONFIGURATION
The controller type for all the above DAC motors should be
selected as DAC on the Motors screen of the
configuration editor. Unit numbers (for unit/channel
configuration) are assigned starting with unit 0 for the first
DAC motor controller selected on the Devices screen. Channel
numbers also start at zero.
The second alternate motor parameter screen is important for
certain DAC configurations. Type little m twice to
get to that screen. To select particular features for the DAC
motor, enter the appropriate strings from the list below as
"Generic Parameters". (To enter a string, type a
single quote '. To delete an entry, type
^D.)
|
-
twelve - twelve-bit DAC
sixteen - sixteen-bit DAC
binary - binary output
twos - two's complement output
bipolar_2.5 - output from -2.5V to +2.5V
bipolar_5 - output from -5V to +5V
bipolar_10 - output from -10V to +10V
unipolar_2.5 - output from 0 to +2.5V
unipolar_5 - output from 0 to +5V
unipolar_10 - output from 0 to +10V
|
|
For the mutually exclusive options, the last one in the list of
generic parameters will take precedence. The default data
configuration is 16-bit binary. The selection of unipolar versus
bipolar and range is only used to configure PCI and USB device
registers, when such hardware configuration options are
available. Selections not supported by the hardware will be
ignored.
The first four parameters should not be used with PCI or USB
devices. spec can determine which model is
being used by the device IDs and knows what output format is
associated with a particular model.
Values in the following table for the steps-per-degree and
user-offset parameters will put the user units in Volts (the
range notation is as above):
|
-
Range Steps/Unit Steps/Unit Offset
(12 bits) (16 bits)
bipolar_2.5 819.15 13107.15 -2.5
bipolar_5 409.55 6553.55 -5
bipolar_10 204.75 3276.75 -10
unipolar_2.5 1638.3 26214.3 0
unipolar_5 819.1 13107.1 0
unipolar_10 409.5 6553.5 0
|
|
For example, for a 16-bit DAC with a range of -10 to +10 Volts,
to have the user units be Volts, set the steps-per-unit parameter
to 3276.75 and the user offset to -10.
As of spec release 5.09.02-2, the following
DAC motor controller configurations are obsolete. One of the
above interface types needs to be chosen instead. The mode (12-
or 16-bit and binary or two's complement output) is selected
using the generic parameters described above.
|
-
DAC 12-Bit D/A (ISA - binary output)
DAC 16-Bit D/A (ISA - binary output)
DAC 12-Bit D/A (ISA - two's complement)
DAC 16-Bit D/A (ISA - two's complement)
|
Likewise, the motor channel controller types
DAC_B12, DAC_B16, DAC_T12
and DAC_T16 are obsolete and need to be replaced
with DAC.
FUNCTIONS
spec includes the following functions to
access the digital I/O capabilities available with some DAC
devices. These functions are currently available for the
Measurement Computing PCI and USB devices.
The following options are associated with the operation of a
particular unit, not with a particular channel. The
mne argument is necessary for the syntax of
the command and should be the mnemonic or motor number of any of
the configured channels associated with the particular card or
device.
motor_par(mne, "io_config" [,
val]) - Configures input/output
direction on the digital I/O lines. The meaning of
val varies with model. For the Measurement
Computing USB-4300 series and PCI-DAC670x series, bits set in
val will be configured as outputs on the
digital I/O lines. On power up, all lines on these devices
default to inputs. Also, note, the configuration cannot be read
from the device. On start up or after a reconfig be
sure to reestablish the configuration before accessing the ports.
When the command is issued without an argument,
spec will return the current value as set by the
user.
For the Measurement Computing PCI-DDA series cards with 48
digital I/O lines, the input/output control is split into four
groups of eight and four groups of four. All lines in each group
are either input or output. Configuration is accomplished by
assigning val the sum of the values in the
first column in the table below. Bits set in
val will set the associated group of lines as
outputs.
|
-
-
val Output Lines
0x01 16 - 19
0x02 8 - 15
0x04 20 - 23
0x08 0 - 7
0x10 40 - 43
0x20 32 - 39
0x40 44 - 47
0x80 24 - 31
|
-
The configuration is readable, and spec will
read the configuration for these devices on start up and after a
reconfig. When the command is issued without an
argument, spec will return the current value.
motor_par(mne, "set_bit",
val) - Set output line corresponding
to bit number
val to high, where bits and
lines are numbered starting from 0.
motor_par(mne, "clr_bit",
val) - Set output line corresponding
to bit number
val to low, where bits and
lines are numbered starting from 0.
motor_par(mne, "put_byte",
val) - Sets output lines
corresponding to the bits set in
val to high
and bits not set in val to low. For the
Measurement Computing PCI-DDA series, affects lines 0 to 7.
motor_par(mne,
"put_byte#", val)
- As above, but allows access to bytes 0 to 5 of the
Measurement Computing PCI-DDA series, which has 48 lines of
digital I/O. The argument
# is the byte
number.
motor_par(mne, "get_bit",
val) - Returns 1 or 0 based on
whether the input line corresponding to bit number
val is high or low, where lines and bits are
numbered starting from 0.
motor_par(mne,
"get_byte") - Returns an 8-bit value that reflects the
setting of the input lines. A set bit correspond to a high-level
on the input. For the Measurement Computing PCI-DDA series,
returns the state of lines 0 to 7.
motor_par(mne,
"get_byte#") - As above, but allows
access to bytes 0 to 5 of the Measurement Computing PCI-DDA
series, which has 48 lines of digital I/O. The argument
# is the byte number.
![[Help File Index]](../../images/index.gif)
... Meeting the software needs of scientists since 1985 ...
Last Formatted Jan 24, 2012
Last Updated 04/28/11
Send comments, queries, suggestions to
info@certif.com
© 1995-2003 Certified Scientific Software. All rights reserved
|
|
