PMODIA_RM Datasheet, PDF (2/3 Pages) List of Unclassifed Manufacturers – Digilent PmodIA™ Impedance Analyzer Reference Manual

PmodIA Reference Manual
Note: The pointer must be set prior to using
block write or block read protocols.
You can perform a block write protocol in a
similar fashion to setting a pointer. Send the
block write command (10100000, or, 0xA0) in
place of the pointer command, and the number
of bytes being sent (represented as a byte) will
take the place of the register address with
subsequent data bytes being zero indexed.
Use the same two protocols when reading data
from the PmodIA: receive byte and block read.
Connector J1 – I²C Communications
Pin Signal Description
1, 2 SCL
I²C clock
3, 4 SDA
I²C data
5, 6 GND Power supply Ground
7, 8 VCC Power supply (3.3V/5V)
Table 1. Interface Connector Signal Description
Clock Source
The PmodIA has an internal oscillator that
generates a 16.776MHz clock to run the
device. You can use an external clock by
loading IC4 on the PmodIA and setting bit 3 in
the control register (register address 0x80 and
0x81).
The PmodIA schematic provides a list of
recommended oscillators. The schematic is
available from the PmodIA product page at
www.digilentinc.com.
Setting up a Frequency Sweep
The electrical impedance, ܼ, of a circuit can
vary over a range of frequencies. The PmodIA
allows you to easily set up a frequency sweep
to find the impedance characteristics of a
circuit.
First, you must set up an I²C interface between
the host board and the PmodIA. The PmodIA
requires three pieces of information to perform
a frequency sweep: a starting frequency, the
number of steps in the sweep, and the
frequency increment after each step. The
starting frequency and the increment per step
parameters are stored as 24-bit words. The
number of steps parameter is stored as a 9-bit
word.
You can program the peak-to-peak voltage of
the output frequency in the sweep by setting
bits 10 and 9 in the control register.
Once the circuit has been excited, it takes
some time to reach its steady state. You can
program a settling time for each point in the
frequency sweep by writing a value to register
addresses 0x8A and 0x8B. This value
represents the number of output frequency
periods that the analog-to-digital converter will
ignore before it starts sampling the frequency
response. (See Table 2 for a list of registers
and their corresponding parameters.)
Frequency Sweep Parameter Storage Registers
Register Address
0x80, 0x81
0x82, 0x83, 0x84
0x85, 0x86, 0x87
0x88, 0x89
0x8A, 0x8B
Parameter
Control register (Bit-10
and Bit-9 set peak-to-
peak voltage for the
output frequency).
Start frequency (Hz)
Increment per step (Hz)
Number of steps in sweep
Settling time (Number of
output frequency periods)
You can calculate the 24-bit word to store at
the register addresses for the start frequency
and the increment per step parameters using
the start frequency code and frequency
increment code equations below. You can
also find these equations and more information
in the AD5933 data sheet.
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