HP 750 - Manual (Page 50)

5-8 Functional Overview C4705-90000
The main PCA ROM contains the following types of information:
D Programs.
D Program constants.
D Character sets.
D Demonstration plot(s).
The main PCA DRAM is used to store the following types of information:
D Variables.
D Temporary constants.
D Plots.
As a plot is received from an external controller by way ofone ofthe plotter interfaces, it is
stored in DRAM. When the complete plot is in DRAM, the main processor converts it, one
swath at a time, to a format suitable for storage and sends it to swath RAM by way of the
processorĆsupport ASIC. A swath has variable height (depending on the print mode) and
extends from border to border across the width of the plot. The processorĆsupport ASIC
extracts the plot data from the swath RAM, converts it to pixels, and sends the pixels serially
by way ofthe trailing cable to the carriage ASIC on the carriage PCA.
Part ofthe cartridge shutdown circuitry is on the main PCA. The cartridges are shutdown:
D When the +5V falls below a certain value (during powerĆup/down).
D When the carriage ASIC asserts shutdown during an access cartridges command.
D Between swath printing.
D When idle.
Carriage PCA
The carriage PCA contains an ASIC that controls the operation ofthe cartridge drivers that
switch power pulses from the ASIC to fire the cartridges. The carriage board also provides
feedback to the main PCA for the current position of the carriage assembly. A lineĆsensor
module mounted on the carriage PCA senses the lines produced by the cartridges and is used
for cartridge alignment. The line sensor also provides an edgeĆsensing capability used to
identify the media loaded in the plotter. VoltageĆsensing circuitry senses deviations in the
cartridge voltages supplied to the print heads and sends signals to the voltage regulators on
the main PCA.
The carriage processor and the printĆcontrol ASIC on the carriage PCA are driven by a
12.288ĆMHz, onĆboard clock. At powerĆon time, the main PCA reset circuit delays the
operation ofthe print control ASIC until the +5 V reaches a steady state.