HP LaserJet II Serie Manual De Instrucciones página 108

HP 33440/HP 33449 COMBINED SERVICE MANUAL
ASIC (Application Specific Integrated CMp)
The AppUcation Specific Integrated Chip (ASIC) is a custom-built integrated chip designed to assist
the main microprocessor in formatting print image information. The ASIC has NO subsystems:
the dynamic memory controuer and hardware assist logic, and the video direct memo~ access
control. As the dynamic memory contro~er, the ASIC controls most DRAM access. The video
direct memo~ portion of the ASIC prepares and provides serialized video dati that is to be used
for the print engine's laser subsystem.
CPU (Central Processing Unit)
This block contains a 16-bit microprocessor (Motorola 68000) that executes instructions stored in
ROM to control operation of the Interface/Formatier PCA. The processor operates from a 9.83
~Z clock.
EPROM/ROM (Erasable Programmable Read Only Memory/Read Only Memory)
Besides storing the microprocessor control programs, the ROM (2 ~yte Read Only Memory)
stores internal character set patierns. Early units will be shipped with six l-Mbit EPROMs and
three 4-~it ROMs. Most units will have four 4-Mbit ROMs instiled.
NVRAM (Non-Volatile RAM)
The ~ is a non-volatfle random-access memory with a capacity of 1024 bits. Since its
contents are not lost when power is switched off, it is used to store printing setup configuration
information entered via the Control Panel and page count information.
DRAM (Dynamic Random Access Memory)
The DRAM consists of 1024 ~ytes of memo~. The memory can be expanded by increments of 1
or 2 ~ytes up to a toti of 4 Mb@s by instifing accessory memory PCAS. This memory stores
printing and font information input from the host system. The DRAM dso serves as a temporary
storage area for print image (dot) data prior to the data being sent to the print engine to create an
image on the photoconductive drum.
Font Cartridge Interface
"Font tiridges" are ROM cartridges which hold additiond dot pattern data for different fonts or
contain ROM code to overlay internal ROM. The font cartridge interface buffers the main bus from
the font cartridge connectors.
Note For the HP 33449, functions described for the HP 33440 following the DRAM
&
description are included under various headings above.
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