An on-chip breakpoint unit of an integrated circuit device is connected to receive the contents of an instruction pointer register via an address communication path. The breakpoint unit has a breakpoint register configured to hold a breakpoint address at which the normal operation of the CPU is to be interrupted for diagnostic purposes, and a comparator circuit operative to compare the breakpoint address with the contents of the instruction pointer register and to issue a breakpoint signal on a breakpoint signal path when there is a match. The on-chip breakpoint unit also has circuitry configured to inhibit generation of the breakpoint signal for a next instruction to be executed upon resumption of normal operation of the CPU after it has been interrupted.