EVAL-AD5933EB

Preliminary Technical Data

Rev. PrC | Page 18 of 32

‘The DDS is going to output 15 cycles of the output excitation voltage before the ADC will start sampling

‘the response signal. The settling time cycle multiplier is set to x1

SettlingTimebyte0 = 0F ‘15 cycles (decimal) = 0F hex

SettlingTimebyte1 = 00 ’00 = X1

WritetToPart &H8B, SettlingTimebyte0

WritetToPart &H8A, SettlingTimebyte1

‘-------------------------------------- PLACE AD5933 IN STANDBYMODE ----------------------------------------

‘Standby mode command = B0 hex

WritetToPart &H80, &HB0

'------------------------- Program the system clock and output excitation range and PGA setting-----------

‘Enable external Oscillator

WritetToControlRegister2 &H81, &H8

‘Set the output excitation range to be 2vp-p and the PGA setting to = x1

WritetToControlRegister2 &H80, &H1

‘-----------------------------------------------------------------------------------------------------------

‘------------- ------------ Initialize impedance under test with start frequency ---------------------------

'Initialize Sensor with Start Frequency

WritetToControlRegister &H80, &H10

msDelay 2

'this is a user determined delay dependant upon the network under analysis (2ms delay)

‘-------------------------------------- Start the frequency sweep ------------------------------------------

'Start Frequency Sweep

WritetToControlRegister &H80, &H20

'Enter Frequency Sweep Loop

ReadbackStatusRegister = PortRead(&HD, &H8F)

ReadbackStatusRegister = ReadbackStatusRegister And &H4 ' mask off bit D2 (i.e. is the sweep complete)

Do While ((ReadbackStatusRegister <> 4) And (Increment <> 0))

'check to see if current sweep point complete

ReadbackStatusRegister = PortRead(&HD, &H8F)

ReadbackStatusRegister = ReadbackStatusRegister And &H2

'mask off bit D1 (valid real and imaginary data available)

‘-------------------------------------------------------------------------

If (ReadbackStatusRegister = 2) Then

' this sweep point has returned valid data so we can proceed with sweep

Else

Do

‘if valid data has not been returned then we need to pole stat reg until such time as valid data

'has been returned

‘i.e. if point is not complete then Repeat sweep point and pole staus reg until valid data returned

WritetToControlRegister &H80, &H40 'repeat sweep point

Do

ReadbackStatusRegister = PortRead(&HD, &H8F)

ReadbackStatusRegister = ReadbackStatusRegister And &H2

' mask off bit D1- Wait until dft complete

Loop While (ReadbackStatusRegister <> 2)

Loop Until (ReadbackStatusRegister = 2)

End If

'-------------------------------------------------------------------------

RealDataUpper = PortRead(&HD, &H94)

RealDataLower = PortRead(&HD, &H95)

RealData = RealDataLower + (RealDataUpper * 256)

'The Real data is stored in a 16 bit 2's complement format.

'In order to use this data it must be converted from 2's complement to decimal format

If RealData <= &H7FFF Then

' h7fff 32767

' Positive

Else

' Negative

'

RealData = RealData And &H7FFF