Canon LBP-1120 Service Manual page 34

2. Operation
When the power is switched ON, the printer enters the WAIT period.
When the printer exits the WAIT period and is ready to operate, the engine controller sends ready status to the
interface controller to notify that it is ready to print.
On receiving the ready status, the interface controller sends a pickup command to the engine controller.
When the engine controller receives the pickup command, it starts the operation of the initial rotation (INTR)
sequence. In this sequence, print paper is picked up and brought to a specified position. Detecting that the paper has
reached the specified position, the engine controller starts sending the /BD signal to the interface controller.
In response, the interface controller sends the VIDEO signals (/VDO, VDO) to the laser driver via the engine
controller, making the VIDEO signals synchronized with the /BD signal.
The engine controller generates LASER CONTROL signals (CNT0, CNT1) and sends them to the laser driver.
The laser diode emits the laser beam when the /VDO signal is "L", CNT0 signal is "H", and CNT1 signal is "L."
The laser beam is scanned by the scanning mirror to form a latent image on the photosensitive drum.
The latent image on the photosensitive drum is transferred onto the paper by the electrophotographic process, and
the paper is delivered to the face up delivery slot.
The STATUS COMMAND signal (/SC) is a bi-directional signal used for serial data transfers between the interface
controller and engine controller.
The interface controller and engine controller send data using the /SC signal; the interface controller sends 16-bit
serial data as a command to the engine controller, and in response, the engine controller sends 16-bit serial data as a
status to the interface controller.
The command and status are synchronized with the SYNCHRONOUS CLOCK signal (/SCLK) output from the
interface controller at the following timing:
When the interface controller outputs data to the engine controller;
• The interface controller outputs the /SC signal synchronizing with the falling edge of the /SCLK signal.
• The engine controller inputs the /SC signal synchronizing with the rising edge of the /SCLK signal.
When the engine controller outputs data to the interface controller;
• The engine controller outputs the /SC signal synchronizing with the falling edge of the /SCLK signal.
• The interface controller inputs the /SCLK signal synchronizing with the rising edge of the /SCLK signal.
The interface controller can perform the software reset on the engine controller by keeping the
/SCLK signal "L" for 2 seconds. The /RESET signal is used to initialize the interface controller at the power-ON. The
signal is sent to the interface controller from the engine controller.
CHAPTER 2
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