General; Cpu(Centrd Processing Unit); Rom(Read-Only Memory); Nvram (Non-Volatile Wndom Access Memory) - HP LaserJet II Serie Manual De Instrucciones

HP 33440/HP 33449 COMBINED SERVICE MANUAL
5-5.
B NTERFACEsYsTEb4
General
For both the HP 33440 ("Interface PCX') and HP 33449 ("Formatter PC#'), the
Interface/Formatter PCA is responsible for the following
Communicating with the host system, either through the standard serial or parallel ports or
through the optional 1/0 interface, if instiled.
Monitoring operator interface via the printer's Control Panel and displaying printer status
information to the operator.
Communicating with the print engine (DC Controller PCA).
Storing font information.
Storing configuration information.
Manipulating incoming data, such as conversion of ASCH character dati into a binary page
image that the print engine may use for creating a laser image on the photoconductive drum.
In addition, for the HP 33449 only, the Formatier PCA contains circuitry for Resolution
EnhancementTM capable of modulating the DC Controller PCA'S laser drive circuitry to produce
"smoothe&' black-to-white boundaries.
Optional mrtridges may dso be ins~ed in connectors on the Interface/Formatter PCA to
provide additiond fonts for text printing or to overlay portions of machine code (ROM) for printer
emulation. Proper communication betieen the Interface/Formatter PCA and the host system
is established by conf~ration settings selected at the Control Panel. ASCII code and graphics
data from the external device is then processed according to the Control Panel settings or printer
commands and is converted to dot data. The dot data is used for modulating the laser.
Descriptions of Blocks in the HP 33440 Interface PCA Diagram
The HP 33440 Interface PCA Block Diagram is shown in Figure 5-17,
CPU (Central Processing Unit)
The CPU block contains a 16-bit microprocessor that executes programs stored in ROM to control
the operation of the Interface PCA.
ROM (Read-Only Memory)
Besides storing microprocessor control programs, the ROM stores the dot patierns of internal
character sets. Maximum ROM capacity is 1 Mbyte.
NVRAM (Non-Volatile Random Access Memory)
The ~ is a non-volatile random-access memory with a capacity of 32 bfies.
contents are not lost when power is switched off, it is used to store printing setup
information entered via the Control Panel and page count information.
SRAM (Static Random Access Memory)
Since its
configuration
The 4 ~yte SRAM is used as a stick area in the 16 Mbyte address space accessed by the
microprocessor (CPU).
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