Agilent Technologies 54502A Manual de Serviço descarregar pdf (Página 91)

Memory The memory of the logic analyzer consists of three separate memories: one ROM

and two RAMs. The system (EP)ROM is 64K long by 8 wide and is used primarily

for booting-up the system and self-test storage. The system (D)RAM is 1M long

by 8 wide and contains the operating system and the acquired data from the target

system. Since the RAM is a volatile memory, the operating system is loaded

loaded at each power-up of the instrument via the built-in disk drive and a mini

floppy disk.

The display (D)RAM is 64K long by 4 wide and is cycle shared between the 68000

and the display refresh cicuitry. This is why the display bus is separate from the

local bus. The two buses are separated by a set of address multiplexers and data

buffers.

CRT Controller The CRT controller provides the synchronization and timing signals needed by the

CRT Monitor Assembly to drive the CRT.

The controller generates four signals: Horizontal sync, vertical sync, display

enable and a 6.25 kHz signal. The horizontal and vertial sync signals are applied to

the CRT monitor assembly and to display PALs. The display PALs use the sync

signals to generate the timing signals for the display RAM.

The CRT Monitor Assembly consists of the sweep board circuitry, a 9-inch white

phosphor display CRT, and the CRT yoke. The assembly requires + 5 and + 12

volts, which it receives from the power supply via the System Board Assembly.

Disk Controller The disk controller performs the necessary functions for reading or writing data to

the built-in disk drive of the logic analyzer. The disk controller interface to the

68000 is an 8-bit bidirectional bus for data, status, and control word transfers.

The built-in disk drive is a 3.5-inch double-sided Sony disk drive. The main

features of the disk drive are low power consumption, low height, and high

reliability with simple mechanism and electronic circuitry.

Keypad and Knob

Interface

The keypad and knob interface provide the circuitry to latch and send the keypad

and knob data to the 68000.

The keypad is elastomeric and each key has a single function.

RS-232-C

Interface

The controlling IC of the RS-232-C Interface is a Signetics SCN2661 Enhanced

Programmable Communications Interface (EPCI), a universal

synchronous/asynchronous receiver/transmitter (USART) data

communications IC.

The SCN2661 serializes parallel data from the 68000 for transmission. At the same

time, it also receives serial data and converts it to parallel data characters for the

68000.

The IC contains a baud rate generator which can be programmed from the logic

analyzer I/O menu for one of eight baud rates. Protocol, word length, stop bits

length, and parity are also programmed via the I/O menu.

Service HP 1650B/1651B

6-4 Service Manual

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Agilent Technologies 54502A Manual de Serviço Página 91

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