A printing unit allows connection of two or more signal sources, thereby improving the efficiency of use of the printing unit. For this purpose the printing unit or printer has a first image signal source for supplying a first image signal. The first image signal source is connectable with a second image...http://www.google.com/patents/US5140675?utm_source=gb-gplus-sharePatent US5140675 - Printer controller apparatus interfacing with external data sources
