APP015.TXT  TestPoint Application Note


APP015.TST  Associated Source File 


(c) Capital Equipment Corporation 1995





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TestPoint Creates a GP-IB Bus Analyzer





A simple IEEE-488 bus analyzer can be created using TestPoint and any 


of CEC's IEEE-488 cards.  


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IEEE-488 bus analyzers can be classified in three, somewhat 


overlapping  categories, as instruments that provide-





   - Data capture only.  These are sufficient for detecting 


     incorrect syntax and command sequences. 





   - IEEE-488 command and data sequences with some triggering 


     and history features.  Most analyzers provide these 


     capabilities. 





    -Timing and sequence relationships between any combination 


     of signals on the bus together with various triggering 


     options and a buffer to provide a command history.  This is 


     best done with a logic analyzer and none of  the 


     commercially available IEEE-488 bus analyzers provide all 


     of these capabilities. 





The combination of an IEEE-488 card with TestPoint allows us to 


capture data, provide conditionals for triggering on specific 


data sequences, and provide a data history which can be 


displayed or stored to disk.  It will not capture the status of 


the dedicated bus management lines SRQ, IFC and  EOI.  Even with 


this restriction,  almost all IEEE-488 problems are related to 


command sequence or syntax,  allowing this analyzer to provide 


help in solving most problems. 





The analyzer is configured by setting the GP-IB interface chip 


to participate in every bus transaction as a listen always 


device.  This is done with a code object and our GPIB DLL. When 


a data byte is available on the bus, itās read, displayed and 


placed in a buffer which can be written to a file selected by 


the user.  Additional displays and conditions can be added as 


desired to enhance the analyzer. 





TestPoint is multitasking and supports multiple GP-IB cards.  A 


PC with two GP-IB cards provides a low  cost controller and 


analyzer in one package.