Each port has a set of status registers to monitor its current state or flag current or historic fault conditions. Two types of status registers exist: latch-value and real-time. The latch-value status registers latch and hold the active value of a field or bit until it is cleared by writing a 1 to that bit (to clear a latched field, the entire field must be written with 1s). Reading these registers allow historic events to be captured by software. A read of the real-time status registers returns the current values of the associated status flags.