Evaluate: MAX1284
Sampling
Choose the desired sampling rate (QSPI™ Clock),
sampling size (Sample! menu item), and press Begin
Sampling! (in Sample! pop-up window). Sample size is
restricted to a power of 2 to permit FFT processing
once the data is saved to a file. After the samples have
been collected, the data is automatically uploaded to
the host and graphed. Once displayed, the data can
be saved optionally to a file.
Saving Graphs to Disk
Data in the real-time graph and in sampled data graphs
may be saved to a file. Only the raw output codes are
saved, but voltages may be inferred, based on the ref-
erence voltage and the maximum code value.
Evaluating Shutdown
The evaluation software configures the 68HC16’s QSPI
submodule to continuously read data from the
MAX1284 into the 68HC16. The sample rate is con-
trolled by the QSPI clock. To evaluate power-saving
modes, these automatic updates must be stopped.
First, set the QSPI clock control to STOP. This reconfig-
ures the 68HC16’s QSPI submodule to stop driving the
serial clock. Second, in the evaluation software’s main
window, uncheck the Read Every...msec checkbox. If
evaluating the hardware shutdown, move jumper JU2
to the 2-3 position.
Reference Voltage
The evaluation software assumes a 2.5V reference volt-
age, unless otherwise specified. Refer to the MAX1284
data sheet for more information. To override this value,
type the new reference voltage into the Vref edit box
and press the Set Vref button.
Detailed Hardware Description
The MAX1284 (U1) is a high-speed, 12-bit data-
acquisition system. Resistor R1 (1kΩ) and capacitor C1
(0.01µF) form a single-pole, low-pass anti-aliasing filter
with a nominal 10µs time constant and a corner fre-
quency of approximately 16kHz. C3 and C4 bypass the
analog-to-digital converter’s (ADC’s) voltage reference.
When plugged into the 68HC16MODULE, the V
DD
cir-
cuit is powered by +5V (Figure 1; refer to the MAX1284
IC data sheet).
Troubleshooting
Problem: No output measurement. System seems to
report zero voltage or fails to make a measurement.
1) Check the V
DD
supply voltage.
2) Check the reference voltage using a DVM.
3) Use an oscilloscope to verify that the conversion-
start signal is being strobed. Verify that SHDN is
being driven high.
Problem: Measurements are erratic, unstable; poor
accuracy.
1) Check the reference voltage using a DVM.
2) Use an oscilloscope to check for noise.
3) When probing for noise, keep the oscilloscope
ground return lead as short as possible, preferably
less than 1/2in (10mm).
MAX1284 Evaluation Kit/Evaluation System
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