digital module 314 is in the mode of operation where the ling is performed junk data from the adc might enter dac due to testing similarly the undetermined data may enter the dac from affect the bist scan testing as such the first isolation unit 316 r between these mixed signal components to avoid the transfer of ral purpose i o gpio pins provide a flexible parallel interface that of custom connections and are used for this purpose these gpio for functional characterization testing of analog module 312 illustrates the schematic of the second isolation unit 318 connected at digital module 314 and the second digital module 322 in this on is required for the control signals such as virtual bus vbus us signals i e read data write data clock ready ready byte accordance with the change back acknowledgment cba standard thus the external serial control interface couples to the second isolation unit 318 to provide these signals a serial to parallel converter 318 a couples to a format converter and post processing unit 318 b a multiplexer 318 c couples to receive the processed serial interface signals along with the internal parallel control interface signals the parallel test control signal pt provides control from multiplexer 318 c this isolation is required when bist scan testing is performed the second digital module 322 and functional testing is being performed upon the first digital module 314 since the output from second digital module 322 may contain junk data isolation is necessary to shield the first digital module 314 advantages of this design include but are not limited to a structure and testing of a mixed signal core on an soc ic at a reduced test time over conventional mixed signal.