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The Bitstream shifter is an utility that provides an interactive interface to the selected TAP, enabling quick state transition and test vector application / response capturing. As illustrated in figure 1, this utility provides shortcuts to the following test actions:
  • TAP selection (upper left)
  • Quick state transition, by selecting the required destination state and clicking on the "State" button
  • Elementary state transition, by clicking on the "TMS0" or "TMS1" buttons
  • Shift in (test vectors) and shift out (test responses) operations through the "Shift" button and the selected TX (for the test vector to be shifted in) and RX (test responses) fields 

Fig. 1: Bitstream shifter window displayed by JTAGer.

The Bitstream shifter utility provides an easy way to carry out interactive test control / observation of one or two BS chains. However, if the test experiment is to be repeated or if proper documentation is required, then a better alternative is to build a test code source file and execute it from the main JTAGer window.