Abstract: An image forming apparatus includes a memory that stores therein a control program, a central processing unit that executes the control program stored in the memory, a print engine controlled by the central processing unit, and a unit that is selected from a plurality of units. An identification signal generating unit generates identification data indicating a type of the unit. An exclusive OR unit allocates an exclusive OR data of an address data for the central processing unit to access the memory and the identification data to the memory.

Abstract: An image forming apparatus includes a memory that stores therein a control program, a central processing unit that executes the control program stored in the memory, a print engine controlled by the central processing unit, and a unit that is selected from a plurality of units. An identification signal generating unit generates identification data indicating a type of the unit. An exclusive OR unit allocates an exclusive OR data of an address data for the central processing unit to access the memory and the identification data to the memory.

Abstract: A density measuring unit is provided for measuring a density of a printing substance such as ink or toner fixed on a paper sheet and producing a value of the printing substance's density. Further, a determining unit is provided for determining whether or not the value of said printing substance's density obtained from the density measuring unit is lower than a predetermined value. The density of the printing substance measured by the density measuring unit is either a density of the printing substance representing a predetermined mark which has been printed in addition to printing out received image information or a density of said printing substance representing said received image information. A blockage removal unit is provided for performing a blockage removal operation for removing any blockage which prevents a printing unit from normally printing out the received image information.