Evaluates: MAX1238
MAX1238 Evaluation Kit
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Read ADC
The Read ADC button manually reads the MAX1238
while using the current setup and configuration byte set-
tings. When the AutoRead checkbox is checked, the
software automatically reads the MAX1238 approxi-
mately every 300ms. AutoRead allows users to modify
the setup and configuration bytes on-the-fly without hav-
ing to manually press the Read ADC button each time.
Setup Byte
The Setup Byte always begins with a start bit value of
one. The SEL2, SEL1, and SEL0 bits control the state
of the reference. The CLK bit selects either internal
clock or external clock mode. The UNI/BIP bit selects
either unipolar or bipolar mode. Setting RST to zero
resets the configuration register. The setup register
remains unchanged. The X Don’t Care bit can be
ignored. Refer to the MAX1238 data sheet for more
information on the SEL2, SEL1, and SEL0 bits within
the Setup Byte.
Config Byte
The Config Byte always begins with a start bit value of
zero. The SCAN1 and SCAN0 bits select the scanning
mode. The CS3, CS2, CS1, and CS0 bits select one of
the 12 analog input channels. The SE/DIFF bit selects
either single-ended or differential mode. Refer to the
MAX1238 data sheet for more information on the
SCAN1, SCAN0, CS3, CS2, CS1, and CS0 bits within
the Config Byte.
Reference Voltage
The evaluation software assumes a +4.096V reference
voltage, unless otherwise specified. To override the
internal 4.096V reference value, ensure bit SEL2
equals zero and bit SEL1 equals one within the Setup
Byte. Then, apply the new reference voltage at the
VREF pad on the board, type in the new reference volt-
age, without the volt unit, and press the Set V
ref
button.
The EV kit software uses the value typed in the V
ref
field
to translate the digital code to a voltage.
Keyboard Navigation
When you type on the keyboard, the system must know
which control should receive the keys. Press the TAB
key to move the keyboard’s focus from one control to
the next. The focused control is indicated by a dotted
outline. SHIFT + TAB moves the focus to the previously
focused control. Buttons respond to the keyboard’s
SPACE bar. Some controls respond to the keyboard’s
UP and DOWN arrow keys. Activate the program’s
menu bar by pressing the F10 key, and then press the
letter of the menu item you want. Most menu items have
one letter underlined, indicating their shortcut key.
Detailed Description
of Hardware
The MAX1238 is a 12-channel (six differential-channel)
12-bit ADC with a 2-wire serial interface. The open-col-
lector inverter (U2) interfaces the PC parallel port to the
2-wire serial interface. U2 and the associated circuitry
are only required when interfacing to the parallel port.
Power the MAX1238 EV kit from a +5VDC power sup-
ply. To prevent damage to the MAX1238 EV kit, do not
exceed +5.5VDC on the supply.
User-Supplied 2-Wire Interface
The MAX1238 EV kit provides a proven PC board lay-
out and software to evaluate the features of the
MAX1238. The Windows software only supports a
2-wire serial interface in S-Mode. To evaluate the
MAX1238 with a user-supplied 2-wire serial interface in
F-Mode or HS-Mode, do the following:
1) Disconnect the MAX1238 EV kit from the PC parallel
port.
2) Install 3kΩ resistors at locations R5 and R7. (This
resistor value may require optimization for each
system.)
3) Connect the user-supplied 2-wire bus to the SDA,
SCL, and GND pads. (Connect to the GND pad
nearest the 5V pad on the MAX1238 EV kit board.)
4) Refer to the MAX1238 data sheet to ensure all tim-
ing specifications are met.
