Simplified Description Of Circuits - HP 650C User Manual

SIMPLIFIED DESCRIPTION OF CIRCUITS

HP C2858A/59A DesignJet 650C circuits communicate with an external controller by way
of either a Centronics or an RS-232-C interface. If an approved modular input/output (MIO)
printed circuit assembly (PCA) is installed, the circuits can communicate by way of an HP-
IB interface or be connected to a network. The main processor reads Centronics, HP-IB, and
Ethernet communications through the port it uses to read memories (ROM or DRAM).
RS-232-C communications are handled by a universal, asynchronous, receiver-transmitter
(UART) and baud rate generator built into the processor support application-specific inte-
grated circuit (ASIC).
HP DesignJet 650C plotters accept plots in Hewlett-Packard Graphics Language (HP-GL),
Hewlett-Packard Graphics Language 2 (HP-GL/2) or Hewlett-Packard Raster Transfer Lan-
guage (HP RTL) form. The main processor converts the plot into an internal format and
stores the entire plot in its dynamic random-access memory (DRAM). Then it transfers the
plot a swath at a time into the swath RAM by way of the processor support ASIC.
On the main PCA, the processor support ASIC is designed to manipulate swath data into the
actual firing order for the pen nozzles on the four pen cartridges that are mounted on the car-
riage assembly. The processor support ASIC receives pixels from the physical swath RAM
and sends them serially to the carriage ASIC.
A main processor on the main PCA controls all plotter operations with the help of the proces-
sor support ASIC and the servo processor. Communications between the servo processor and
the main processor take place through registers in the processor support ASIC.
The processor support ASIC provides pulse-width-modulated signals to the Y -axis motor
driver and the X-axis motor driver to drive the Y -axis (carriage) motor and the X-axis (paper)
motor. The linear encoder connected to the carriage PCA gives the processor support ASIC
feedback about the position of the carriage. The X-axis motor encoder on the X-axis motor
gives the processor support ASIC feedback about the position of the X-axis motor.
In addition, the processor support ASIC contains a DRAM controller that generates multi-
plexor control and enable strobes for the DRAM row and column addresses during a memory
access. The DRAM controller also arbitrates between a memory request and a refresh re-
quest, and it performs the refresh operation.
The servo processor communicates with the main processor through registers in the proces-
sor support ASIC. The servo processor writes information into the registers and sends an in-
terrupt to the main processor. The main processor then reads the registers and the interrupt is
automatically cleared. Using this procedure, the servo processor provides the main processor
with information from the plotter sensors. The sensors give the main processor the ability to
check status conditions.
5-2 Functional Overview