HP DeskJet 1200C printer architecture - includes related articles on use of solid modeling CAD system in design, on how reusable packaging and rugged design can minimize environmental impact, and on a new model for product development - HP DeskJet 1200C and HP DeskJet 1200C/PS ink-jet printers - Technical

Hewlett-Packard Journal, Feb, 1994 by Kevin M. Bockman, Anton Tabar, Erol Erturk, Robert R. Giles, William H. Schweibert

The second major decision was to implement a language independent interface to the print engine. Traditionally, our print engines were tightly coupled with the language system. Because of the need to support PostScript as well as PCL 5C as native on the printer, a technique was required for both languages to communicate with the print engine in an independent way. This allowed concurrent development of both PostScript and PCL 5C so that they could be introduced simultaneously. It also permits a high level of language code reuse on different products. This language independent interface has now been implemented successfully in three printers and is described in the article on page 85.

To meet the needs of the mainstream office, the interface to the computer world needed to be flexible. The unit is shipped with a built-in high-speed Centronics interface that is expected to meet most of the needs of the IBM-compatible PC world. To meet the needs of other computing platforms and interface technologies, an HP MIO port was also added. This MIO port implements version 5.0 of this HP standard interface. For operation in mixed environments, the system implements "hot" I/O switching. After the end of a job or after a specified amount of time with no activity, the processor releases the active port and begins polling for I/O requests from both ports. Once I/O is detected, the inactive port is blocked and data is received from the active port.

The last major design decision is the implementation of a print mode forecaster to help meet the throughput requirements. The print mode forecaster looks at the next 2/3 inch and determines from the data whether to print in one pass or three passes. It also predicts the most intelligent paper movement so that the maximum amount of data can be printed at one time without compromising the quality of the print (for example, the forecaster never splits text or graphics in the high-quality mode). It is the responsibility of the forecaster to pick the optimum motion path for both vertical and horizontal movements. It also manages swath RAM and controls the Resolution Enhancement technology (RET) that is implemented in the hardware. This is a very complex module consisting of approximately 7000 lines of code.

Conclusion

Given the challenges of media independence, speed, print quality, low cost, and a fast development cycle, the Deskjet 1200C team used the new seamless engineering model and concentrated on doing a thorough job from the beginning. This allowed all of the major areas--mechanical, electrical, and computer--to architect a system with the flexibility and margins to meet its goals.

Acknowledgments

A program of this size had many contributors. We would like to thank all those who contributed to its success. There are far too many to name and many have been named in other articles. We would especially like to thank the following: Bill Hilliard for the firmWare architecture and tremendous firmware support for the rest of the project, Mike Harless for the I/O firmware, Gary Gragg for the product diagnostics and the manufacturing line tests, Steve Mueller for his PostScript contributions, Jeff Sunamoto for his commitment and technical breadth, Cary Enslow for the mechanical, Graciela Gomez for the electrical, and Toby Cowger for the firmware designs on the front panel, Steve Hend_ricks for the electronics sheet-metal enclosure, Ron Kaplan for the product enclosure, Dick Kemplin for his innovative chassis design, Bill Meyer, John Thomas, and Bob Haselby for their design and management of the analog portions of the electronics and sensors, Tim McDonough and Phil Schultz for the digital design portion of the project, Joe Fiske for his communication support between the Deskjet 1200C work team and the engineering staff, Jim Ruder and Phil Faraci who played key roles in the definition of the new product development model, and Oscar Padilia for creating many of the sketches used in this article. Special thanks go to the Deskjet 1200C work team without whose diligence and support we would not be producing products today, and to Tao Ngo who lent his technical support throughout the project.