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Chapter 8: Theory of Operation
Block-Level Theory
8–4
Acquisition System
The acquisition system includes two attenuator assemblies, acquisition board, and scope
interface board. The attenuators condition the signal, which is then digitized and stored by the
acquisition board. The scope interface board provides the system control interface from the
motherboard, and also interfaces the acquisition board to the SVGA display board for display of
the acquired data. More detailed theory on the acquisition system follows this top-level block
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 30 keys, all dedicated to a single function to improve ease of use. A
conductive element on the inside of each key closes a gap on the underlying keyboard circuit.
The keyboard controller detects this short and sends the proper keypress information to the
system controller on the motherboard.
There are eleven dedicated knobs. 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 Remote Inhibit sense line that is routed to the power
supply. When closed, there is an impedance of approximately 196
Ω to ground from the Remote
Inhibit sense line; the power supply detects this and turns on or off as required.
Disk Drives
The flexible disk drive is 1.44 Mbyte, MS-DOS compatible. It is located on the front panel. The
disk drive can be used to load a new oscilloscope operating system or to load application-specific
software. This disk drive is only available on older Infiniium oscilloscopes.
The LS-120 flexible disk drive is 120 Mbyte, MS-DOS compatible. It is located on the front panel.
The disk drive can be used to load a new oscilloscope operating system or to load application-
specific software. This disk drive is available on newer Infiniium oscilloscopes or those Infiniium
oscilloscopes that have been upgraded.
The hard disk drive is a 2.5" high-capacity, shock-resistant unit. It is used to store the oscilloscope
operating system and certain system configuration data.
Either drive can also be used to store and recall instrument setups and waveforms.
Attenuators
The attenuators provide the appropriate impedance matching and all the attenuation and gain
selection for each input channel. They connect directly to the acquisition board and are fastened
to the acquisition board with screws.
Motherboard
The motherboard provides all system control and interface functions for the instrument. It
contains a CPU, ROM, RAM, keyboard and mouse interfaces, serial and parallel interfaces, hard
and floppy disk drive interfaces, and interfaces to the IBM-PC industry compatible ISA (Industry
Standard Architecture) and PCI (Peripheral Component Interconnect) buses.