•
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Display Assembly
Circuit
Description
The OSM
is
primarily used
as
a synchronous bus for setting
up
the internal
register bits of the GCS, HS, preamp and DACs on the analog board.
The
SIM module does all of the chip selecting for all of the addressable ICs
on the processor board.
U201
has three types
of
support circuitry. The first
type
is
pull-up resistors for
IRO
lines and for configuring the processor boot
up. The second type
is
a crystal oscillator. The crystal oscillates at
32
kHz.
The processor uses a phase
lock loop to create a 16 MHz system clock from
this
crystal. The third type
is
a power-on reset circuit. The reset circuit,
consisting
mainly
of
U207,
is
a passive circuit that monitors VCC. When the
power
supply exceeds
4.5V,
U207 releases the reset line allowing the pro-
cessor to run.
If VCC drops below 4.5V a reset occurs.
ROM/RAM Subsystem A5
<3>
The ROM/RAM sUbsystem consists
of
256 kb
of
Flash ROM, 256 kb of static
RAM,
and 64 kb of non-volatile static
RAM.
The Flash
ROM
has a require-
ment which states that it must not have an
OE during a write cycle. Conse-
quently, the gates of
U221
in
this subsystem prevent this from happening.
Readout Subsystem A5
~
The readout subsystem consists of a custom readout IC, two DACs, a 2.5 V
reference voltage, and some support resistors and capacitors for compensa-
tion and
filtering. The readout
IC
has an internal
RAM
into which the proces-
sor puts ascii characters. The processor
also controls the state of the read-
out
IC
for calibration, cursor positioning, and update rate. The readout
IC
itself then drives the vertical and horizontal DACs
as
well as the blanking.
Front-Panel Interface Subsystem A5
<P
The front-panel interface subsystem consists
of
U215 (DUART), and its
3.686 MHz
crystal. The processor communicates to the front-panel proces-
sor through an
RS232 like interface. This interface
is
maintained by the
DUART,
running at 9600 baud. The DUART
is
connected to
IR05
on the
processor.
U201
talks
to
U215 using data lines D8 through D15.
Analog Board Interface Subsystem A5
<p
The analog board interface subsystem consists
of
an
ECl
to CMOS convert-
er and a
CMOS to
ECl
converter. The SGMAIN lines coming from the ana-
log board are ECL. These lines were converted to CMOS by using two
transistors and a
couple
of
resistors.
All
information (waveforms, text, and cursors) is displayed by the
A3
Display
Driver board. It generates the high voltages necessary to drive the
CRT.
It
also
contains the vertical and horizontal amplifier circuitry.
TAS 475 and TAS 485 Service Manual
3·5
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