I will be using eight analog outputs on the 6715 card, and programming in VC++. Four of the outputs will be at a constant voltage, the other four will be a 50% duty cycle pwm signal. I will need to ramp up the pwm frequencey of all four outputs together, hold them contant for a short time, and then quicky change the frequency of only one output. I fear that defining the array of values for all eight outputs for the required length of time will be too large for the onboard memory buffer. Can computer memory be used instead when calling DAQmxWriteAnalogF64? TIA Eric
Actually, the computer memory is always used in transfers. The driver automatically creates a PC buffer for each task. It then determines the best way to write this information to the card's FIFO (yours is 8192 samples, see the datasheet for more info). There are, of course, ways to manually control this behavior, such as the "use onboard memory only" property, or the "do not allow regeneration" property, which prevents the DAC from outputting old data. The latter property requires your application to continuously supply new data - it will not repeat existing data, as in the default behavior. Please let us know if you have any additional questions.
Hope this helps,
Ryan Verret Product Marketing Engineer Signal Generators National Instruments