Theory of Operation
4–14
1735 HD High Definition Waveform Monitor
The front-panel Light-Emitting Diode (LED) matrix is driven by U33 through
U34. Each individual LED’s data is written in when /WR and the data input
(U34, pins 2–9) are low. Data is latched when /WR goes high. LED refresh
occurs continuously.
NOVRAM.
U42 and U35 form the master microprocessor NOVRAM (non-volatile
memory) that retains the current front-panel and auxiliary control status. Data is
written in and read out through pins 3 and 4; the master microprocessor controls
data in and out along with providing the serial clock. Each RAM has its own
enable provided by the master microprocessor. These three lines (Clock,
Read/Write, and Enable) are activated when the power is turned on, when any
front-panel switch is pressed, or when a store/recall is requested.
U38 detects the loss of instrument power in time for the NOVRAM to execute a
save operation. When the +5 V supply drops a few hundred millivolts, pin 7 is
pulled low, causing the NOVRAM to store the current status. The front panel
and auxiliary control data is saved in milliseconds when the power starts to drop
below safe operating levels for the NOVRAM. U41 is a three-terminal regulator
operating from the +13 V supply. As soon as the +13 V raises enough to provide
a +5 V output from U41, the NOVRAM recalls the data saved so that it is
available to the microprocessor when all supplies are up to their operating
tolerances.
Master to Readout Interface.
The CRT readout is drawn with a series of dots. Port
4 of the master microprocessor (U33) defines the horizontal component of the
readout dot, while port 5 defines the vertical component of the dot. U39 and U36
are current output DACs. U43A and B convert the readout DAC output current
to voltage.
R156 and R145 adjust the position of the readout on the CRT. Readout gain
adjustments are in the horizontal and vertical amplifier circuits. The horizontal
and vertical readout is enabled by ROEN from Port 6 of U33.
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Страница 20: ...Getting Started...
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