For the benifit of those builders that will have their NimbleSig III projects completed in advance to the publishing of part III of my QEX article I decided to post this information here as it will be needed to get the generators and power meter running properly.

EEPROM Initial Programming


As the NimbleSig III firmware needs initialization values from EEPROM during start up or after reset it will not function properly if the EEPROM is blank. The only time this will normally happen is when a new NimbleSig III module is is run for the first time. It is thus necessary to pre-program the EEPROM to default values prior to calibrating a new module for the first time. The XC, XE and XK commands are provided for this purpose.


Enter the “XC” command which will ask for the nominal DDS clock frequency which normally is 500 MHz. This frequency must be entered in Hz. When requested enter 500000000 (ie number five followed by eight zeros). The software will acknowledge that the clock value is saved.


Next enter the “XE” command and confirm that you wish to proceed. Again the software will acknowledge the saving of approximate calibration data.


Next enter the “XI” command and confirm that you wish to proceed with a 'c' when requested followed by “19” to load the default register settings. Again the software will acknowledge the saving of approximate calibration data.


Finally enter the “XK” command and again confirm you wish to proceed. And again acknowledgement of data saved will be given for approximate calibration of both generators.


Once the above EEPROM initialization steps are completed re-start the NS3 module by either power cycling or reseting which is needed to load the default data from the EEPROM into the MPU data memory.


For confirmation enter the “XR” command which provides a screen dump of the DDS registers. A screen dump similar to that shown below should follow. Note values for registers A & B at addresses 4h should be 147AE148h and 1999999Ah respectively. The values for registers at 6h are output level calibration sensitive thus may vary but they should be in the range of 1100h to 1200h. There should be 40 and 50 MHz signals present at the outputs of generators “A” and “B” respectively at levels close to -10 dBm. The “LA10” power level command should report a level less than -50 dBm. If both generator outputs and power meter indications are normal plus the screen dump compares favorably to register dump shown below the module is ready for calibration.

NimbleSig III Register Dump in HyperTerminal

73 de VA7TA