5-6
Phaser 440 Color Printer
5
Theory of Operation
CPU
Phaser 440 print engine CPUs consist of a microprocessor, ROM, RAM and a
clock circuit. The CPU is the heart of the print engine. It controls the timing
controller, the mechanical controller, and print engine diagnostics.
Interface buffers
The interface buffers receive data from the image processor board, where the
image data was received from the host computer and processed into data for the
print engine. The interface buffer routes received data signals to the data
controller.
Data controller and line buffers
The data controller receives input data from the interface and stores it in a data
buffer. The data buffer contains two buffers: one buffer holds the current line of
image data being transmitted to the print engine and the other buffer holds the
preceding seven lines of image data received by the print engine. When the data
buffers contain all eight lines of data, then the data controller transfers the data
to the heat controller.
Heat controller (dot compensation)
Each thermal heating element must receive sufficient energy to vaporize dye
properly. Too much energy and the dye dot smears when printed. Too little
energy, and the dye dot is ill-formed and does not adhere to the paper. In the
heat controller, the data of the current raster line to be printed is compared with
previously printed lines. The dot compensator determines when, and for how
long, the individual thermal head elements should be energized to properly
vaporize dye onto the paper. This comparison accounts for the thermal energy
stored in each heating element from its previous dot printing action as well as
the thermal energy picked up from adjacent heating elements.
In this comparison, the heat controller determines, for each dot to be printed, if
the heating element was used to print any dots during the few lines, and also if
any neighboring dots were or will be printed next to the dot in question.
Knowing this history, the heat controller can determine how long to sustain the
voltage pulse to the dot's heating element to correctly print the dot. This
information is transferred to the line memory buffer.
