For each value register in a register pair, there is a mask register of the same format. Setting a bit to 1 in the mask register has the effect of making the corresponding bit in the value register disregarded in the comparison.

For example, when a watchpoint is required on a particular memory location, but the data value is irrelevant, the data mask register can be programmed to 0xFFFFFFFF, all bits set to 1, to ignore the entire data bus field.

Setting the mask bit to 0 means that the comparator matches only if the input value matches the value programmed into the value register.