A programmable logic device includes a functional block, which does not form part of an embedded processor, which can perform a testing function on other functional blocks of the programmable logic device. Thus, the test block can read stored data values from registers in the other functional blocks of the programmable logic device, or can read signal values at points in the other functional blocks of the programmable logic device, or can insert specific data values in registers in the other functional blocks of the programmable logic device.