This is a program for the STM32F4 Discovery board with a custom shield carrying a AD9910 DDS chip. The device is designed to run in cycles between to different modes. During the setup mode it is receiving information via Ethernet from a remote control program. Once all data is received the program switches into run mode. In this mode all communication is disabled to prevent interrupts. In this mode the program waits for an outside trigger on which it changes the settings of the DDS chip based on the previously send information. Once all output has been written the program switches back into the setup mode.

The settings of the DDS chip can be changed via two different ways. Via serial communication different registers of the DDS can be changed which become active on a trigger pulse. Alternatively parallel communication can be used to change 16 bit of a single register with an update frequency of up to ~22 MHz (processor speed / 6).

Via serial communication registers for frequency output or of the ramp generator can be changed while the program is running. The chip will write the data to the DDS immediately, but they remain inactive until a trigger signal is received. This can be repeated multiple times, e.g. to generate a complex frequency ramp by reprogramming the ramp generator.

The changes become active immediately after triggering, however there is a minimal delay between two triggers which is required for the processor to write the next set of values.

Parallel communication allows to update a single register while the DDS chip is running. The limiting update frequency is the processor speed combined with the limited amount of RAM to store the data. The program waits for an external trigger on which it starts writing the programmed data to the external output. There is a time delay between sending the trigger on reaction of the processor of one interrupt cycle.

• Measure update time in serial mode

• Interupt delay: ~400ns