Agilent Technologies 01664-97005 1664A Theory, System Memory, CRT Controller and Display RAM

Theory of Operation

The 1664A Logic Analyzer

1664A Theory

CPU

Located on the main circuit board, the microprocessor is a Motorola 68EC020 running at 25 MHz. The microprocessor controls all of the functions of the logic analyzer including processing and storing data, displaying data, and configuring the acquisition ICs to obtain and store data.

System Memory

The system memory is made up of both read-only memory (ROM) and random access memory (RAM). A single 128Kx8 EPROM is used as a boot ROM (boot-up requires operating system on disk loaded in the disk drive). Four 1Mx4 DRAMS are configured to provide a 1Mx16 DRAM space.

On power-up, instructions in the boot ROM command the instrument to execute its boot routine, which loads the operating system from disk. The boot routine (on disk) includes power-up operation verification of the instrument subsystems and entering the operating system. The CPU searches for the operating system on disk.

The DRAM stores the instrument configuration, acquired data to be processed, and any inverse assembler loaded in the instrument by the user.

CRT Controller and Display RAM

A Brooktree BT476KPJ66 RAMDAC color palette and a National Semiconductor LM1882CM video frame generator control the CRT. One of the RGB outputs of the color palette provides the eight-shade grey scale display. The video frame generator provides the horizontal and vertical synchronization timing signals.

The display RAM is made up of two 256Kx4 DRAMS configured as 256Kx8 and stores all of the pixel information used by the color palette. A serial address counter and an address multiplexer control the DRAM addressing. At the conclusion of each video frame the vertical sync signal from the video generator resets the serial address counter and a new frame is generated.

Disk Drive Controller

The disk drive controller consists of a single floppy drive controller IC. The floppy drive controller provides all signals to the disk drive including read and write data, read and write signals, write gate, and step signal. The floppy drive controller also reads status signals from the disk drive, including a track 00 signal, disk ready, and disk change signal.

Keypad and Knob Interface

The front panel keypad is scanned directly from the microprocessor address bus during the video blanking cycle of the CRT. When a front panel key is pressed the associated address bits are fed to the data bus through the pressed key and read by the microprocessor.

The rotary pulse generator (RPG) knob is part of the HIL circuitry. Pulses and direction of rotation information are directed to an RPG interface IC and then to the HIL loop. The microprocessor then reads and interprets the RPG signals and performs the desired tasks.

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