HP 8550 Service Manual - Page 234
Control panel, contrast to suit his/her preference.
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Control panel The control panel consists of the PCBs shown in figure 128 on page 233 and a liquid crystal display (LCD) capable of displaying images in 320 by 240 dots, and has the following functions: l Data communication l LCD processing l LCD contrast adjustment l Touch switch input processing Data communication The communication of data is controlled by the CPU on the reader controller PCB. LCD processing The CPU on the reader controller PCB provides the control panel CPU PCB with data (display data) as instructed by the program. The data is moved through the control panel CPU PCB to the LCD panel. LCD contrast adjustment The control panel is equipped with a dial to enable the user to adjust the contrast of the LCD. The user may turn the dial to adjust the contrast to suit his/her preference. Control panel CPU The control panel CPU has the following functions: l Monitoring the key inputs (communicates keypad and function key inputs to the CPU on the reader controller PCB) l Controlling the buzzer sound l Turning off and on the control panel LEDs 232 Chapter 5 - Theory of operation EN