1. A breakpoint logic unit for a data processing apparatus, comprising: a value storage operable to store data indicative of a selected value for an operational characteristic of the data processing apparatus; comparator logic operable to compare said selected value with a value of said operational characteristic as generated by the data processing apparatus and to generate at least one result signal indicative of a match between said value and said selected value; a control storage operable to store a match control value, if the match control value has a first value the comparator logic being operable to set the at least one result signal if a match is detected between said value and said selected value, whilst if the match control value has a second value the comparator logic being operable to set the at least one result signal if a match is not detected between said value and said selected value; and breakpoint generation logic operable to enable generation of an associated at least one breakpoint signal if the at least one result signal is set.