Pattern placement for high speed printers

In a page printer, the controller has to generate the whole print page as a bitmap, where characters and images can be placed on each point and rotated in each 90° orientation. Building up this bitmap for printing is one of the most time-critical procedures in a printer of the speed range over 150 pages/min. The solution to this problem of addressing all points can be done by a general-purpose processor for printers in the range of 8-20 pages/min, or by the combination of a general-purpose processor and an image-processor in the range of 12-80 pages/min. Controllers for high-speed printers (50-300 pages/min) generally contain a combination of general-purpose and image processors plus a lot of dedicated hardware built up in gate arrays. In the controllers of Siemens high-speed laser printers three different memories are involved in printing a page. The first is named the matrix memory where the bitmaps of the characters and the digitized images are stored in 32-b words. For an optimal usage of the memory the characters and images are reduced to the smallest rectangle and stored without an alignment to the byte border. The second is a rotation memory, a matrix of 32-b by 32-b memory cells which can be read out in all four 90° orientations. The last is the page dot memory, where the digitized page is stored in 64-b words