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-3100 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.