Crt Monitor Assembly; Main Assembly; Disk Drive; Attenuators - HP 54520 Series Service Manual

Chapter 8: Theory of Operation
Block-Level Theory
CRT Monitor Assembly
The CRT Monitor assembly consists of the sweep board circuitry, a 9-inch green phosphor
CRT, and the CRT yoke. The assembly requires +5 V and +12 V from the power supply via the
main assembly.
The noninterlacing raster display is controlled by the CPU portion of the main assembly.
System control provides synchronization and pixel information.
Main Assembly
The main assembly contains the acquisition system and system control circuitry. It provides
interfaces for the attenuators, power supply assembly, CRT monitor assembly, keyboard, disk
drive, HP-IB, and RS-232. The vertical inputs are the output of the attenuator assemblies.
The auxiliary trigger input is directly to the main assembly through a cable from the rear
panel, The user interface is through the front-panel keyboard or with a controller via the
HP-IB connector on the rear panel. A more detailed theory of the main assembly follows block
level theory.
Front Panel
The front panel is read and controlled by a microcontroller IC. This device contains a
microprocessor, RAM, ROM, and a DUART for communication with the microprocessor on the
main assembly. The microcontroller is located on the keyboard and communicates with the
system control circuitry through a cable and RS-232 interface. It reads the keys and knobs
and controls the LED indicators.
The elastomeric keypad has 48 keys: 17 single-function keys, 24 multi-function keys, and 7
softkeys with functions that depend on the displayed menu.
There are six knobs: five dedicated to specific functions and another that controls the function
selected by the softkeys. Each knob controls a mechanical switch. The output of the switch
is a 2-bit gray code that is read by the microcontroller for direction and distance turned.
A pushbutton controls the power through a shaft to the line filter on the rear panel.
Disk Drive
The flexible disk drive is a 1.44 Mbyte and DOS compatible. It is located on the front panel.
The disk drive can be used to load a new oscilloscope operating system into the flash ROM or
load application specific software. It can also be used to store and recall instrument setups
and waveforms.
Attenuators
The attenuators are the channel interface to the front panel. They provide the appropriate
impedance matching and all the attenuation and gain changing. They connect directly to the
main assembly and are fastened to the main assembly with screws,
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