HP Color LaserJet CM4730 Service Manual - Page 194

Memory tag The memory tag is a nonvolatile memory that is built into the print cartridge. It stores information about the amount of toner in the cartridge and estimates the remaining life. Figure 4-26 Memory tag on page 174 illustrates how the memory tag operates. Memory tag contact Memory tag Memory data DC controller PCB Memory controller PCB Cartridge Figure 4-26 Memory tag The DC controller reads information from the memory tag whenever the MFP is turned on, whenever the top cover is closed, and whenever it receives a read command from the formatter. The DC controller writes information to the memory tag at specified times during a print operation, whenever it receives a write command from the formatter, and after print completion. If the DC controller is unable to either read to or write from the memory tag four times in a row, the DC controller alerts the formatter of a memory tag abnormality. Cartridge presence detection The MFP detects the presence of print cartridges when the power is turned on or the door is closed. There are two procedures to the cartridge presence detection: ● Memory tag detection ● Photosensitive drum detection Memory tag detection The DC controller reads the data in the memory tag and determines the cartridge presence. If the reading fails, the DC controller goes to the next procedure, photosensitive drum detection. Photosensitive drum detection The DC controller measures the torque of the photosensitive drum. The DC controller stops the drum motor after driving it for the prescribed period of time. If the motor stops rotating within the specified period after the stoppage command is sent, the DC controller detects the cartridge presence based on the large load torque. If it takes more than the prescribed period of time for the motor to stop, the DC controller detects the cartridge absence based on the small load torque. When the DC controller detects the cartridge absence, it stops the engine and notifies the formatter. Figure 4-27 Photosensitive drum detection on page 175 illustrates the drum detection procedure. 174 Chapter 4 Theory of operation ENWW