ICS AOB8/12, Руководство по эксплуатации продукта

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Manual Number: 00650-134-4 Page 9
Chapter 5: Programming
Programming the AOB16/12 and AOB8/12 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) preload
(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*4096/5+2048);
would output “Volts” volts to channel “ch”, assuming a bipolar 5V range. For other bipolar
ranges, substitute the positive Full-Scale-Volts in place of “5” in the equation. For unipolar
ranges, remove the “-2048” and use the appropriate FSV in place of the “5”;
Upon power-up, or hardware reset, the DAC registers are restricted to a save value and the card is
set in Simultaneous Update mode. Since the preload 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 is 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 to the BASE+8 address. (Alternatively, a read to BASE+10 will update the DAC regis-
ters 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 preload registers causing all
outputs to be updated and changed simultaneously.
Automatic Update Mode is the configuration which 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 to BASE+2 address will change the card back to Automatic Update Mode without
updating the outputs. Or, a read to BASE+10 will update all outputs simultaneously and then release
the card to the Automatic Update Mode.
Restrict-Output-Voltage is a unique addition to our DAC card which resets the DAC’s in a manner
similar to a hardware reset without changing the operating mode. This is done by sending a read to
Base A14. Since the preload registers are not cleared the previous outputs will be restored
from the preload register when a “Clear Restrict-Output-Voltage” command is issued by a write to
Base Address +15.