HP LaserJet 4 Service Manual - Page 145

Basic Sequence of Operation The Formatter PCA and the DC Controller PCA share information during printer operation. Connector J7 on the formatter and connector J207 on the DC controller form a link which operates as a serial data bus. This allows printer status, command information, and dot-image data to be passed between both controllers. Standard Printer Operation The following events take place during normal printer operation: 1 After the printer's power is turned ON, the printer enters the Warmup period. 2 After the printer completes the Warmup period and is ready for operation, the DC controller sends a READY signal (RDY) to the formatter. 3 After the RDY signal is true and print data is ready to be transmitted, the formatter sends a PRINT signal (PRNT) to the DC controller. 4 After the DC controller receives the PRNT signal, the Initial Rotation period begins. 5 At the end of the Initial Rotation period, the DC controller sends a TOP OF PRINT signal (TOP) synchronized with a BEAM DETECT signal (BD) to the formatter. This initiates the Print period. Functional Overview 5-33