HP LaserJet 4 Service Manual - Page 114

DC Controller System The DC Controller PCA is responsible for coordinating all activities involved in the printing process. The DC Controller enables the drive circuitry for the laser beam, and coordinates print data from the Formatter PCA with paper size, laser beam motion, the high voltage system, fuser temperature, and motors. The DC Controller also shares machine status information with the Formatter PCA so that proper diagnostic messages are displayed on the control panel. The DC Controller communicates with the Paper Control PCA, the High Voltage PCA, the Envelope Feeder, Lower Cassette Assembly and Duplex Assembly by way of two serial data lines (SLI and SLO). One line (SLO) is used for sending commands, the other (SLI) is used for receiving status information from the selected devices. The amount of toner in the Toner Cartridge also is monitored indirectly with information on the serial data line. In summary, the following systems and functions are controlled and/or monitored by the DC Controller: • Paper Motion • Laser and Scanner Drive • Timing • Machine Status • Paper Size and Availability • High Voltage System • Fusing Temperature • Main Motor Drive • DC Power Supply • Toner Level 5-2 Functional Overview