Programming 5-1
Chapter 5
Programming
Overview
The PCI-AOB2/4/6 Series’ DACs and Digital I/O use 40 (hex) consecutive I/O addresses.
Programming the cards is very straightforward as there are only two operating modes,
three range-selection switches per channel, and one unique addition. The basic operation
of a Digital-to-Analog card is to write a 12-bit value to a Digital to Analog Converter
(DAC) pre-load (outer) register where it is buffered and loaded by an update command to
a DAC (inner) register. Outputs of that register control a "ladder" network which produces
the analog output. The output voltage range is defined by settings of the range-selection
switches for that channel. In C:
outport (BASE+(CH*2),
(Volts*4096/10)-2048);
would output "Volts" volts to channel "ch", assuming a bipolar 5V range. For other
bipolar ranges, substitute the appropriate voltage span in place of "10" in the equation. For
unipolar ranges, remove the "-2048" and use the appropriate voltage span in place of the
"10".
Upon power-up, or hardware reset, the DAC registers are restricted to a safe value and the
card is set in Simultaneous Update mode. Since the pre-load register is not cleared upon
power-up, but left at an undefined value, a known value must be written to the preload
registers before using a "Clear Restrict-Output-Voltage" command.
Simultaneous Update Mode
The power-up or default mode of operation for the DAC card. When a value is written to a
DAC address the output does not change until an output update is commanded via a read
from Base 8. (Alternatively, a read of Base A will update the DAC
registers and switch the board to Automatic Update Mode.) While in Simultaneous Update
Mode, a single read will load all DAC registers with the value waiting in the pre-load
registers, causing all outputs to be updated and changed simultaneously.
Automatic Update Mode
The configuration that changes a DAC output immediately after the high-byte of the new
value is written to the DAC address. If the card is in Simultaneous Update Mode a read of
Base 2 will change the card back to Automatic Update Mode without updating
the outputs. A read of Base A will update all outputs simultaneously and then
place the card in Automatic Update Mode.
Summary of Contents for PCI-AOB2 Series
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