AVX

POWER SUPPLY

General Description

The MAX125/MAX126 evaluation systems (EV systems)
consist of a MAX125/MAX126 evaluation kit (EV kit) and
a Maxim 68HC16MOD-16WIDE microcontroller (µC)
module. The MAX125/MAX126 are high-speed, 8-chan-
nel, 14-bit data-acquisition systems with four simultane-
ous track/holds. Windows 3.1TM/Windows 95TM software
provides a handy user interface to exercise the
MAX125/MAX126's features.

Order the complete EV system for comprehensive eval-
uation of the MAX125/MAX126 with a personal comput-
er. Order the EV kit if you have already purchased the
µC module (68HC16MOD-16WIDE) with another Maxim
EV system or if you desire custom use in other µC-
based systems.

Stand-Alone EV Kits

The MAX125/MAX126 EV kits provide a proven PC
board layout to facilitate evaluation of the MAX125/
MAX126. The EV kits must be interfaced to appropriate
timing signals for proper operation. Apply dual power
supplies (±8V min, ±20V max) to connector P1, pin 5
(P1-5), and P1-9, with ground at P1-1. Connect the
active-low read strobe to P1-38, the write strobe to
P1-37, the chip selects to P1-35, and the convert-start
signal to P1-36 (Table 1 and Figure 1). Refer to the
MAX125/MAX126 data sheet for timing requirements.

EV Systems

The MAX125/MAX126 EV systems operate from a user-
supplied +13V to +20V DC power supply. Windows
3.1/Windows 95 software running on an IBM PC inter-
faces to the EV system board through the computer's
serial-communications port. The software can be oper-
ated with or without a mouse. Refer to the

Quick Start

section for setup and operating instructions.

____________________________Features

Proven PC Board Layout

Complete Evaluation System Samples to 40ksps

Convenient Test Points Provided On Board

Data-Logging Software with FFT Capability

Fully Assembled and Tested

Evaluate: MAX125/MAX126

MAX125/MAX126 Evaluation

Systems/Evaluation Kits

________________________________________________________________

Maxim Integrated Products

PIN

P11

MAX126EVB16

System Component List

Ordering Information*

P15

P19

P135

P136

P137

PART

MAX125

EVKIT

MAX125EVB16

0°C to +70°C

TEMP. RANGE

INTERFACE TYPE

User Supplied

Windows Software

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.

MAX126

EVKIT

MAX126EVB16

0°C to +70°C

User Supplied

Windows Software

Windows 3.1 and Windows 95 are trademarks of Microsoft Corp.

PART

QTY

DESCRIPTION

MAX125EVKIT

MAX125 evaluation kit

68HC16MOD-16WIDE

68HC16 µC module with
16-bit parallel interface

PART

QTY

DESCRIPTION

MAX126EVKIT

MAX126 evaluation kit

68HC16MOD-16WIDE

68HC16 µC module with
16-bit parallel interface

The MAX125 software can be used only with the complete eval-
uation system (MAX125EVB16 or MAX126EVB16), which
includes the 68HC16MOD-16WIDE module together with the
MAX125EVKIT or MAX126EVKIT.

Table 1. Power-Supply and Timing Signal
Connections

P138

SIGNAL

Ground

Positive Supply, +8V to +20V

Negative Supply, -8V to -20V

Chip Select

Convert-Start

Write Strobe

Read Strobe

MAX125EVB16

System Component List

19-1322; Rev 0; 10/97

Evaluate: MAX125/MAX126

MAX125/MAX126 Evaluation
Systems/Evaluation Kits

_______________________________________________________________________________________

Quick Start

Recommended Equipment

You will need the following equipment before you
begin:

A small DC power supply (+13V to +20V DC at
250mA)

An IBM PC-compatible computer capable of run-
ning Windows 3.1 or Windows 95

A spare serial-communications port, preferably a
9-pin plug

A serial cable to connect the computer's serial port
to the Maxim 68HC16MOD-16WIDE module

Connections and Setup

Perform the following steps to evaluate the MAX125 or
MAX126:

1) Carefully connect the boards by aligning the two

40-pin headers of the MAX125/MAX126 EV kit with
the two 40-pin connectors of the 68HC16MOD-
16WIDE module. Gently press them together. The
two boards should be flush against each other.

2) Connect a +13V to +20V DC power source to the

µC module at the terminal block (J2) next to the
on/off switch, along the top edge of the µC module.
Observe the polarity marked on the board.

3) Connect a cable from the computer's serial port to

the µC module. With a 9-pin serial port, use a
straight-through, 9-pin female-to-male cable. If the
only available serial port uses a 25-pin connector, a
standard 25-pin to 9-pin adapter is required. The
EV kit software checks the modem status lines
(CTS, DSR, DCD) to confirm that the correct port
has been selected.

4) Install the EV kit software on your computer by

running the

INSTALL.EXE program on the floppy

disk. The program files are copied, and icons are
created for them in the Windows 3.1 program man-
ager (or the Windows 95 Start menu). The EV kit soft-
ware evaluates both the MAX125 and the MAX126.

5) Start the program by opening its icon in the pro-

gram manager (or Start menu).

6) The program prompts you to connect the µC mod-

ule and turn its power on. Slide SW1 to the on posi-
tion. Select the correct serial port and click OK. The
program automatically downloads

KIT125.B16 to

the module. The default device setting is for the
MAX125. If using the MAX126, select "MAX126" in
the device characteristics dialog box and click on
"apply."

DESIGNATION QTY

DESCRIPTION

C1, C2, C4,
C5, C6, C9,

C10

0.1µF ceramic capacitors

C3, C8

10µF, 25V tantalum capacitors

4.7µF, 6.3V tantalum capacitor

C11

100pF ceramic capacitor

P1, P2

2x20 right-angle connectors

R1, R6

100

, 1% resistors

R2R5

10k

, 5% resistors

R7, R8

, 5% resistors

Maxim MAX125 or MAX126

78L05 voltage regulator

74HCT244

79L05 negative-voltage regulator

16MHz clock-oscillator module

None

PC board

None

Software disk:

MAX125 Evaluation Kit

List of Files in MAX125 EV Kit

FILE

FUNCTION

INSTALL.EXE

Installs EV kit files onto your computer

MAX125.EXE

Application program

KIT125.B16

Loads software into the 68HC16 µC

MAX125.HLP

Help file

UNINST.EXE

Removes EV kit files from your computer

MAX125.INI

Program settings

MAX125EVKIT/MAX126EVKIT

Component List

7) Apply input signals to the inputs labeled

CH1ACH4A at the bottom edge of the MAX125/
MAX126 EV kit board. Observe the readout on the
screen.

Detailed Description of Software

The MAX125/MAX126 digitize up to four inputs from
either the A or the B input bank. Conversion time is
determined by the number of enabled inputs. The soft-
ware collects samples at a maximum throughput of
40ksps (one channel) and 26ksps (four channels). The
various program functions are grouped into dialog
boxes, which are accessible from the Window menu on
the main menu bar.

Keyboard Navigation

If a mouse or other pointing device is not available, use
the following keyboard shortcuts (Table 2):

Press ALT+W to display the Window menu, and
then select a tool window.

Press the TAB key to select controls within the
selected tool window.

Activate buttons by pressing the spacebar.

Use the up/down arrow keys for check boxes, radio
buttons, and combo boxes.

Scan Tool

You can automatically take readings at regular intervals
up to 10 samples per second from user-selected chan-
nels by selecting Scan Tool from the Window menu.
The "Channel Selection and Configuration" group con-
trols which channels will be scanned. The "Bipolar and
Differential" controls are disabled because the
MAX125/MAX126's transfer function is bipolar.

The "Scan Rate" combo box controls the rate at which
measurements are made. Readings are displayed in
the "Recent Values" text area.

You may optionally record readings into a data-log file.
Click on the "New Log" button to begin or end data log-
ging. The "Log File Format" dialog box is displayed.
One complete line of data is written after all enabled
channels have been sampled. The first line of the log
file contains the column headings. Each subsequent
line contains all enabled channels, separated by com-
mas, tabs, or spaces (previously selected in the "Log
File Format" dialog box). Once a log file has been
opened, it can be paused or resumed with the corre-
sponding Log menu commands. The program contin-
ues to write data to the log file until the "Stop Log"
button is clicked.

One-Shot Read Tool

The "One-Shot Read Tool" allows direct control of the
analog-to-digital converter (ADC) configuration. Select
the channel and mode of operation to update the
"Control Byte" display. Or, change the "Control Byte"
bits directly and observe the change in the "Channel
Selection" control. The "Read Now" button writes the
configuration information to the ADC and performs one
reading.

Power Cycling Tool

To reduce average supply current demand, the
MAX125/MAX126 can be shut down between conver-
sions. From the Window menu, select "Power Cycling
Tool." The amount of power saved depends primarily
on how long the part is off between conversions.
Conversion accuracy depends on the power-up delay,
reference capacitor, and time in power-down. Adjust
the off-time with the "Delay Between Samples" com-
mand. Adjust the on-time with the "Power-Up Delay"
command.

Using an adequate power-up delay ensures that the
desired conversion accuracy is achieved during power-
cycling modes. The reference must be allowed enough
time to stabilize before the measurement is performed.
Start with zero power-up delay, and increase the delay
time until no further change in accuracy is observed. The
power-up delay requirement depends on the value of the
reference capacitor and the off-time (delay between
samples).

The MAX125/MAX126 EV kit software performs power-
up by writing a configuration word with the shutdown
bit cleared. After power-up, the power-up delay is exe-
cuted to allow time for the reference voltage to stabilize
so that an accurate measurement can be performed.

Evaluate: MAX125/MAX126

MAX125/MAX126 Evaluation

Systems/Evaluation Kits

_______________________________________________________________________________________

Copies the image of the main window
onto the clipboard

ALT+PrintScreen

Clicks on the selected button

Spacebar

System menu of child window

ALT+minus

System menu of main program window

ALT+space

Window menu

ALT+W

Selects next control

TAB

FUNCTION

KEY

Table 2. Keyboard-Navigation Shortcuts

Evaluate: MAX125/MAX126

Sampling Tool

To sample data at rates up to 40ksps, select "Sampling
Tool" from the Window menu, make your selections,
and click on the Start button. Adjust the timing delays
as appropriate to control the sample rate. Estimate the
effective sample rate by taking the reciprocal of the
sum of the delay between samples, the power-up
delay, and the conversion time. Sample size is restrict-
ed to a power of two so that the "Fast Fourier
Transform" (FFT) tool can process the data. "Sample
Size" controls the number of samples collected on
each selected channel. After the samples have been
collected, the data is automatically uploaded to the
host and graphed. Once displayed, the data can
optionally be saved to a file.

FFT Tool

The EV software includes an FFT tool that can display
the spectral content of data collected with the high-
speed sampling tool.

To view the spectral content of a waveform, first select
a data sample that was previously collected with the
"Sampling Tool." Then select "FFT Tool" from the
Window menu. Check the output plots desired and
click on the Start button.

A data-windowing function preprocesses the data
sample before performing an FFT.

When the input sig-

nal is not synchronized to the sampling clock, spectral
energy appears to leak into nearby frequency buckets.
A suitable data window tapers the raw data to zero
amplitude at the beginning and end, reducing this spec-
tral leakage.

Device Characteristics

The "Device Characteristics" dialog box contains para-
meters that are not expected to change often. The
device selection is used to select between the MAX125
and the MAX126.

Evaluating the MAX126

The MAX125 software can evaluate the MAX126 direct-
ly. From the Window menu, select "Device Charac-
teristics." Next, change the device type from MAX125
to MAX126. This tells the program that the input voltage
span is ±V

REF

instead of ±2V

REF

Changing the Reference Voltage

The EV kit software assumes a 2.5V reference voltage,
unless otherwise specified. Apply an external 2.5V ref-
erence to the REFIN pad to overdrive the internal refer-
ence. See the MAX125/MAX126 data sheet for more
information. From the Window menu, select "Device
Characteristics." Next, type the new reference voltage
into the "Reference Voltage" edit box.

Detailed Description

of Hardware

The ADC (U1) is an 8-channel, 14-bit data-acquisition
system with four simultaneous track/holds. Linear regu-
lators U2 and U4 provide clean analog ±5V power sup-
plies for the ADC. R8 and C1 filter digital noise out of
the analog power supply. U3 isolates the CS, RD, WR,
and CONVST signals from the main system bus to fur-
ther prevent digital noise from entering the ADC. R7
and C11 filter the TTL clock oscillator to prevent over-
shoot at the CLK input.

The MAX125/MAX126's chip-select (CS) is memory-
mapped to location 7E000 on the 68HC16 module. This
location is used for writing configuration bytes and
reading data. The convert-start (CONVST) signal is also
memory-mapped and is asserted for one memory-
access cycle when memory location 7E800 is
accessed. The MAX125/MAX126's interrupt (INT) out-
put triggers an interrupt on the 68HC16 through the
input capture vector.

Measuring Supply Current

To monitor supply current, measure the voltage across
resistor R1 (for the +5V supply) or R6 (for the -5V sup-
ply). These resistors are 100

±1%, so every 1mV

across R1 or R6 represents 10µA of supply current.

MAX125/MAX126 Evaluation
Systems/Evaluation Kits

_______________________________________________________________________________________

Check the +5V and -5V sup-
ply voltages.

Check the 2.5V REFOUT ref-
erence voltage using a digi-
tal voltmeter.

Use an oscilloscope to verify
that the 16MHz clock is run-
ning and that the conver-
sion-start signal is being
strobed.

No output measurement.
System seems to report
zero voltage or fails to
make a measurement.

CORRECTIVE ACTIONS

PROBLEM

For more information on the FFT and data-windowing functions, refer to W.H. Press, et al., Numerical Recipes in Pascal: The Art of
Scientific Computing,

Cambridge University Press, 1989, ISBN 0-521-37516-9.

Table 3. Troubleshooting Guide

Evaluate: MAX125/MAX126

MAX125/MAX126 Evaluation

Systems/Evaluation Kits

_______________________________________________________________________________________

CH1A

CH1B

CH2A

CH2B

CH3B

CH3A

CH4B

CH4A

CLK

-5V

JU1

C11

100pF

0.1

MAX125

MAX126

P2-4

P2-3

P2-2

P2-1

P1-38

P1-37

P2-8

P2-7

P2-6

P2-5

P2-10

P2-9

P2-14

P2-13

P2-12

P2-11

P1-20

D0/A0

D1/A1

D2/A2

D3/A3

D10

D11

D12

D13

INT

CONVST

DGND

AVSS

CH1A

CH1B

CH2A

CH2B

CH3B

CH3A

CH4B

CH4A

CLK

REFIN

REFOUT

AGND

P1-6

P1-5

GND

N.C.

OUT

GND

N.C.

CS8

CS7

+5V

GND

P1-4

P1-3

P1-2

P1-1

REFIN

4.7

6.3V

REFOUT

DVDD

AVDD

LM78L05ACM

0.1

+5V

10k

100

10k

0.1

+5V

0.1

100

+12V

25V

P1-9

N.C.

GND

OUT

N.C.

-5V

-12V

LM79L05ACM

0.1

C10

0.1

25V

16MHz

OSCILLATOR

74HCT244

U3B

74HCT244

+5V

P1-36

P1-35

CS8/7E800

U3A

CS7/7E000

Figure 1. MAX125 EV Kit Schematic

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