引言

　　本參考設計提供了構建一個示波器所需的全部電路(圖1)，設計采用MAX1396EVKIT (參考設計要求用MAX1393ETB ADC替代MAX1396ETB ADC)和一臺PC，并提供了電路圖、Windows?軟件和微控制器固件。固件示例程序采用C語言編寫，利用IAR Embedded Workbench?平臺針對MAXQ2000進行編譯，可免費下載MAXQ? 1.13C，4K KickStart版本的IAR Embedded Workbench。

　　本文介紹了一個基于PC的示波器參考設計。重點介紹了MAX1393 ADC和MAX1396 EV (評估)板，文中給出了電路圖、軟件及軟件功能說明。

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　　圖1. 基于PC的示波器

　　MAX1393簡介

　　MAX1393為單通道、312.5ksps、真差分、12位SAR ADC。本參考設計采用MAX1393對輸入波形進行采樣。

　　硬件簡介

　　MAX1396EVKIT包括MAX1396 ADC (本設計中將其替換為MAX1393)、MAXQ2000微控制器、所有必需的無源元件以及經過驗證的PCB布局。MAX1396EVKIT原理圖如圖2所示。

　　MAX1396EVKIT的電路板上沒有安裝MAX1393，可通過Maxim網站訂購MAX1393ETB的樣品，替換評估板上的MAX1396ETB。表1列出了所需的跳線設置。

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　　詳細電路圖(PDF, 19kB)

　　圖2. MAX1396EVKIT原理圖

　　表1. 跳線設置

　　JumperPosition

　　JU11-2

　　JU21-2

　　JU31-2

　　JU41-2

　　JU51-2

　　JU61-2

　　JU71-2

　　固件簡介

　　AN4530-firmware.zip文件包含的C程序可以使MAXQ2000的SPI?外設與MAX1393通信。當MAXQ2000采用20MHz系統時鐘時，SPI串行時鐘為5MHz。MAXQ2000從PC機收到命令后，微控制器即刻開始從MAX1393獲取數據。存儲512個采樣數據后，MAXQ2000將數據發送給PC。

　　Windows程序簡介

　　將MAX1396EVKIT通過USB電纜連接到PC機后，固件將等待接收Windows程序命令，如圖3所示。按下Convert鍵接收評估板采集的輸入信號數據，然后顯示數據波形(圖4)。當鼠標光標放置在波形區域時，將在屏幕頂端顯示相應的時間(Time)和電壓(Voltage)，如圖5所示。表2給出了其它軟件功能。

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　　圖3. MAX1393參考設計的Windows程序啟動

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　　圖4. 顯示波形

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　　圖5. 在屏幕頂端顯示時間和電壓

　　表2. 軟件功能
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Button	Description
	Vertically scales the waveform.
	Horizontally scales the waveform.
	Shifts the waveform horizontally.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the starting time at the left of the screen.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the ending time at the right of the screen.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the sampling time.
	Enter a proper trigger-level value into this edit box.
	Click on one of the two radio buttons to choose either rising-edge triggering or falling-edge triggering.
	Press this button to receive input-signal data from the EV kit board and display the waveform on the screen.
	Select this checkbox to receive continuous data from the EV kit and continuous updates to the waveform on the screen.
	Press this button to redraw the waveform on the screen.
	Press this button to exit the program.

Button	Description
	Vertically scales the waveform.
	Horizontally scales the waveform.
	Shifts the waveform horizontally.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the starting time at the left of the screen.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the ending time at the right of the screen.
	Enter a value (in milliseconds) into the edit box and press the Set button to set the sampling time.
	Enter a proper trigger-level value into this edit box.
	Click on one of the two radio buttons to choose either rising-edge triggering or falling-edge triggering.
	Press this button to receive input-signal data from the EV kit board and display the waveform on the screen.
	Select this checkbox to receive continuous data from the EV kit and continuous updates to the waveform on the screen.
	Press this button to redraw the waveform on the screen.
	Press this button to exit the program.