Chapter 12 12-11
Theory of Operation
Digital Control Theory
A1 Front Panel
The A1 front panel assembly provides user interface with the analyzer. It includes the
keyboard for local user inputs, and the front panel LEDs that indicate instrument status.
The RPG (rotary pulse generator) is not electrically connected to the front panel, but
provides user inputs directly to the front panel processor.
A2 Front Panel Processor
The A2 front panel processor detects and decodes user inputs from the front panel and the
RPG, and transmits them to the CPU. It has the capability to interrupt the CPU to provide
information updates. It controls the front panel LEDs that provide status information to
the user.
The A2 also contains the LVDS (low voltage differential signaling) receivers which connect
to the graphics processor. The received video signals are routed to the A18 display.
A9 CPU/A10 Digital IF
The A9 CPU assembly contains the main CPU (central processing unit), the digital signal
processor, memory storage, and interconnect port interfaces. The main CPU is the master
controller for the analyzer, including the other dedicated microprocessors. The memory
includes EEPROM, DRAM, flash ROM, SRAM and boot ROM.
Data from the receiver is serially clocked into the A9 CPU assembly from the A10 digital
IF. The data taking sequence is triggered either from the A14 fractional-N assembly,
externally from the rear panel, or by software on the A9 assembly.
Main CPU
The main CPU is a 32-bit microprocessor that maintains digital control over the entire
instrument through the instrument bus. The main CPU receives external control
information from the front panel or GPIB, and performs processing and formatting
operations on the raw data in the main RAM. It controls the digital signal processor, the
front panel processor, the display processor, and the interconnect port interfaces. In
addition, when the analyzer is in the system controller mode, the main CPU controls
peripheral devices through the peripheral port interfaces.
The main CPU has a dedicated flash ROM that contains the operating system for
instrument control. Front panel settings are stored in SRAM, with a battery providing at
least 5 years of backup storage when external power is off.
Main RAM
The main RAM (random access memory) is shared memory for the CPU and the digital
signal processor. It stores the raw data received from the digital signal processor, while
additional calculations are performed on it by the CPU. The CPU reads the resulting
formatted data from the main RAM and converts it to GSP commands. It writes these
commands to the GSP for output to the analyzer display.
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