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Using the SI_SCOPE RS232 Analyzer with USB <-> RS232 Converters

SI_SCOPE Pro version 4.0 or higher has the ability to utilize your computers USB ports to analyze an RS232 line through the use of a USB <-> RS232 converter. To utilize your USB converter configure SI_SCOPE to use the "Windows API/USB" board type off the "Configure Board Type" menu. After enabling this option configure your ports from the "Configure Port Parameters" menu. This dialog will now prompt you for the Windows port number (COM1, COM2 etc.) instead of the I/O address.

Important: Before using SI_SCOPE with your USB converter it is important to understand the limitations imposed by this configuration. With all other RS232 cards SI_SCOPE will load its own drivers. These drivers have been designed for serial analysis and utilize a common buffer for data/signal events captured from both ports. This special buffering allows SI_SCOPE to preserve the sequence in which data and signal events occur. All USB converters come with a special driver that allows an application to read/write it using the Windows COM API. Since these drivers will use separate buffers for each port it is possible for data/signal events to be displayed out of order on SI_SCOPE's screen. The smaller the latency time  between data from each device the more likely this is to occur. For example if you are examining a serial link where the DCE device sends the string "DCE DEVICE" and upon reception the DTE device waits 2 seconds and responds with "DTE DEVICE" you should not have a problem. As the time interval for the DTE response decreases the likelihood for data to appear out of order increases. The threshold on this reply time will be dependent on the USB converter used. Since the source of the data (DCE/DTE) is always correctly preserved this will only pose a problem if you are trying to reverse engineer a foreign protocol.

Most users have no problem when using this configuration to debug a protocol they designed. However if you are trying to reverse engineer an unknown protocol or if inter character timing is important to your application we recommend using an interrupt driven serial card with or using our UltraTap Cable which connects to your system through a USB port and handles RS232 data capture and time stamping through specialized embedded electronics in the cable.

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This page last updated on 03/29/2011