NAME

DESCRIPTION

spec has built-in C code to treat DAC devices as motors, so that the standard commands to read and position motors will get and set values using the DAC registers. The "move" of a DAC motor is instantaneous - the DAC register is written at once with the value corresponding to the target position. The DAC hardware supported includes ISA boards with either byte or word access, PCI boards with word access and VME modules using A16 addressing mode. (The CAMAC DSP E250, KS 3112/6 and KS 3195 DAC modules are currently configured differently than the modules describe here.)

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)

The only currently recognized PCI DAC cards are the Measurement Computing models DDA08, 6702 and 6703. Recognition for other boards will be added in response to user requests.

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. Special handling for other boards will be added as users request.

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 in the DAC configuration. 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 all DAC types, the steps-per-degree parameter and user- offset parameter should be adjusted to set the range and offsets for user units. For example, for a 16-bit DAC with a range of 0 to +10 Volts, set the steps-per-unit parameter to 6553.6 for the user units to be Volts. For a 12-bit DAC with the same range, set the steps-per-unit parameter to 409.6. For a 16-bit DAC to work from -10 to +10 Volts, set the steps-per-unit parameter to 3276.8 and set the offset between user and dial units to -10.

OBSOLETE CONFIGURATION

The following DAC motor controller configurations are obsolete. One of the above interface types should be chosen instead, and the mode (12- or 16-bit and binary or two's complement output) should be selected using the generic parameters, as 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)