MAX125/MAX126高速数据采集系统EVkit与μC模块全面评测

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MAX125EVKIT-MAX126EVKIT 是一款针对高性能、8通道、14位数据采集系统MAX125和MAX126的评估套件。这款套装包括一个MAX125/MAX126评估板（EV kit）以及一款Maxim 68HC16MOD-16WIDE微控制器模块，用于展示这两款芯片的强大功能和性能。这些系统主要应用于需要快速、高精度数据采集的应用场景，如工业自动化、实验室测试或科学研究。该系统采用Windows 3.1™/Windows95™软件作为用户界面，使得用户能够方便地控制和测试MAX125/MAX126的各种特性，例如跟踪/保持功能，这对于调试和优化设计非常关键。用户可以根据需求选择购买完整的EV系统，或者仅购买EV kit，如果他们已经拥有Maxim的其他EV系统的68HC16MOD-16WIDE微控制器模块，或者希望在基于其他微控制器的系统中定制使用。 EV kits提供了经过验证的PC板设计，确保了评估过程的便捷性。为了实现正确运行，用户需将EV kit与合适的时钟信号连接起来，通过P1端口的pin5（P1-5）和pin9提供±8V到±20V之间的双电源，并确保接地连接在P1-1。此外，还需连接外部读取信号（active-low strobe）到P1-38，写入信号到P1-37，芯片选择信号到P1-35。 MAX125/MAX126 EV kit的独立使用价值在于其灵活性，它作为一个平台，可以与其他微控制器模块无缝集成，为工程师们提供了测试和验证新设计的理想环境。通过这个套装，开发者能深入了解芯片的工作原理，优化接口设计，并在实际应用中实现高效的数据采集和处理能力。 MAX125EVKIT-MAX126EVKIT是一个功能强大的工具，旨在简化高性能数据采集系统的评估过程，无论是对硬件工程师还是软件开发者来说，都是提升项目效率和产品质量的重要资源。

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 100Ω ±1%, so every 1mV

across R1 or R6 represents 10µA of supply current.

MAX125/MAX126 Evaluation

Systems/Evaluation Kits

4 _______________________________________________________________________________________

• 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 ACTIONSPROBLEM

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

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