Functional clock generation controlled by JTAG extensions

摘要

An on-chip clock generation system used the Serial Interface in an on-chip JTAG facility to write bit patterns in a shift register. The bit patterns are applied to control inputs of a clock generation circuit whose clock outputs are varied in accordance with changes to the bit patterns. By using the same facility to provide JTAG and clock functions the output clocks provided by clock generation circuit on the chip can be varied without using additional pins or the output clocks themselves.