I'm working on a frequency hopping application using the AD9910. I need to update the frequency every 1us, so I'm using the parallel port for this with the parallel port destination bits, F[1:0], set to 10b (see Table 4 on page 21 of the datasheet). The amplitude, however, is pretty much static (set once at the start and then leave it the same).
Question 1: How do I set up the AD9910 to get frequency changes from the parallel port, but static amplitude information from the initial setting value in the serial port registers? Or more generally, if the frequency, amplitude, or phase is being set using the parallel port and the serial port, how does the AD9910 know whether to use the parallel or serial port?
Question 2: Also on page 21 of the datasheet, there is a description of the TxEnable functionality. In part of this it states "Furthermore, when the TxEnable pin is held false, the device internally clears the 16-bit data-words ..." So my question is - if I am using the parallel port to set frequency, amplitude, and/or phase parameters and the TxEnable pin is toggled (so that the device internally clears the 16-bit data-words), what happens to the RF output? Does it change when the 16-bit data word is cleared?