A controller for a printer module having a printhead that prints an image on printable media including a low speed central processing unit with associated program memory storing program steps for execution by the central processing unit to operate the printer module and associated scratch memory to store program variables. An image to be printed is stored in an image storage memory of approximately 1.3 Mbytes. An image access unit accesses the image and transfers the image to a printhead interface on command from the central processing unit. The printhead interface transforms the image to a 1600 dpi dithered CMY image for printing by a monolithic printhead. The controller also includes one or more interface units communicating with components of said printer module under control of the central processing unit. A Serial Bus interface communicates with the Serial Bus of a compact printer system to transfer data and power between modules.