In mask programmable integrated circuit, such as a structured ASIC, a delay chain provides a delay that is set by a mask programmable switch. The delay chain receives an input to allow the delay mask programmed delay to be overridden using a JTAG controller. This allows testing of different delays. The input may also be provided by a fuse block, so that the fuse block can override the mask programmable switch, thus allowing a delay to be changes after mask programming.