Power up
7803 controls power up of the unit. There are
three layers to the power up sequence. The first
layer involves the Analog Board and the Front
Panel. The second layer involves the Digital
Board and the BE. The third involves the Front
Panel and the Analog Board.
The first layer controls the first set of switched
supplies. After the System Control
Microcomputer receives its reset, the ISTDBY
control voltage goes Low to turn On the first set
of switched supplies, The SW5Vdc and the
SW8Vdc. It communicates on the I
2
C bus initial-
izing the Tuner, the Audio Decoder, and the
Video/Audio Routing ICs. If they respond proper-
ly, It then communicates on the I
2
C to the Front
Panel Microcomputer. If the Front Panel
Microcomputer responds properly, the ION con-
trol voltage goes Low.
The second layer occurs when the ION switching
voltage comes out of the Analog Board. The ION
control voltage passes through the Digital Board
to the Power Supply and turns On a second set
of switched voltages. These include the 3.3Vdc
supply. The 3.3Vdc supply is the main B+ to
many of the microcomputers throughout the unit.
The System Control Microcomputer then sends
out the IReset signal to 7902 on the Digital
Board. This IC produces a delayed Resetn signal
line for 7200. 7200 activates its I
2
C and provides
several reset and initialization signals for the
Digital Boards and the BE. They all go through a
self test. If the self test succeeds, the VSM com-
municates through UART1 that the system is op-
erating, and the unit can enable the Front Panel
to accept a response. The Front Panel
Microcomputer then places four dashes on the
Front Panel Display. ION goes High placing the
unit in Standby, waiting for keyboard input. This
normally takes 6-8 seconds. The System Control
Microcomputer allows 10 seconds for the UART1
response. If it does not come, the unit goes into
sleep mode, and will not accept keyboard input.
When the Front Panel Microcomputer receives a
keyboard response, it communicates that action
to the System Control Microcomputer to switch
back On the second layer of switched voltages.
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