The electronic control unit (ECU) represents a combination of electronic components and circuits that direct every detail of a printer's operation. A typical ECU is made up of five major sections: a communications interface, driver circuits, a control panel, memory, and main logic. In spite of the diversity between printers and print head technologies, every printer model must include circuitry to handle these areas.
1-18 illustrates each of these key areas in the ECU for an HP DeskJet 500 printer. The exploded diagram of 1-19 shows you the ECU (marked 19), the sepa-rate head driver circuit (marked 15), and the system power supply module (marked 17) in the overall DeskJet assembly. The detailed operation and troubleshooting techniques for an ECU are presented in Chapter 9. A communications interface handles the transfer of all data between the printer and computer. It also manages and coordinates signals ("handshaking") that synchronize data transfer. Data can be transferred over either a "parallel" or "serial" interface. Both interface methods work equally well for most general-purpose printers. Your printer's particular compatibilities are listed in its user's manual. Digital electronics alone is not enough to run a printer. Drivers convert low-power digital signals into voltage and current levels that are needed to operate real-world devices, such as motors, solenoids, and print heads. Drivers also might be used to condition sensor signals for use by digital logic. A control panel allows you to work with the printer directly by operating manual functions (e.g., line feed, form feed, etc.). It also lets you alter various operating modes like font style or character pitch. Indicators are included to display various printer conditions. Your printer's overall operation is organized and managed by the main logic circuits. Decision making is handled by programmable processing components such as microprocessors or microcontrollers. There might be more than one processing component depending on the printer's sophistication. New printers tend to replace a second microprocessor with one or more application-specific integrated circuits (ASICs), which can optimize printer communication and driver functions. Memory devices are needed to retain permanent and temporary information used within the printer. The printer's command language and microprocessor instructions are stored in permanent memory (ROM). Temporary memory (RAM, also called the buffer) is used to hold character and graphic data received by the printer's communication interface.
0 Comments