MAX1280 EV System
The MAX1280 EV system operates from a user-sup-
plied 7VDC to 20VDC power supply. Windows
98/2000/XP-compatible software running on a PC inter-
faces to the EV system board through the computer’s
serial communications port. See the Recommended
Equipment and Connections and Setup sections for
setup and operating instructions.
Description of Software
The evaluation software’s main window controls the
active control word bits, serial clock speed, and sam-
ple rate. It displays the voltage and output code for
each active channel, as well as some statistics of the
input signal. A separate graph window shows the data
changing in real time. The update rate is limited to
about 10 samples per second due to COM port band-
width limitations.
Controls
The control word is divided into several fields. To
change the active control word, drop down the appro-
priate field’s combo box and select the desired option.
If the QSPI™ clock is set to STOP, then configuration
data will not be sent until the READ button is clicked.
Statistics
The Minimum and Maximum fields show the highest and
lowest readings acquired. The Average field shows a run-
ning mean based on the equation a
i
= (k)(x
i
) + (1 - k)
(a
i
-
1
). The Clear button resets the statistics. To remove
offset errors, first apply 0V to the active input channel,
clear statistics, acquire some samples, and then check
Tare. This average offset voltage will now be subtracted
from all subsequent measurements.
Sampling
Choose the desired sampling rate (QSPI Clock), sam-
pling size (Sample! menu item), click 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 collect-
ed, the data is automatically uploaded to the host and
is graphed. Once displayed, the data can optionally be
saved 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.
Scanning All Channels
To scan through all channels, select SCAN from the
INPUT menu.
Evaluating Shutdown
The evaluation software configures the 68HC16’s QSPI
submodule to continuously read data from the
MAX1280 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.
Next, choose the desired software power-down control
word, and click the Read button to send the new con-
figuration to the MAX1280. Or, if evaluating the hard-
ware shutdown, move jumper JU2 to the 2-3 position.
Sense the supply current by measuring the voltage
across resistors R9 and R10.
Reference Voltage
The evaluation software assumes a 2.5V reference volt-
age, unless otherwise specified. Refer to the MAX1280
IC data sheet for more information. To override this
value, type the new reference voltage into the Vref edit
box and click the Set Vref button.
Description of Hardware
U1, the MAX1280, is a high-speed, multichannel, 12-bit
data-acquisition system. Resistors R1–R8 and capaci-
tors C1–C8 form single-pole, lowpass anti-aliasing fil-
ters with a nominal 3ms time constant and approxi-
mately a 50kHz corner frequency. Jumper JU1 con-
nects the analog common (COM) to ground (GND).
C10 bypasses the bandgap reference, and C9 bypass-
es the analog-to-digital converter’s (ADC’s) voltage ref-
erence. When plugged into the 68HC16MODULE,
VDD1 and VDD2 are both powered by +5V. See the
MAX1280 EV kit schematic (Figure 1) and refer to the
MAX1280 IC data sheet.
Evaluate: MAX1280
MAX1280 Evaluation Kit/Evaluation System
_______________________________________________________________________________________ 3
QSPI is a trademark of Motorola, Inc.
COM is disconnected from GND.
common-mode input range.
