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Chapter 8: Theory of Operation
Agilent 1680A,AD-series Logic Analyzer Theory
Power Distribution Board
The power distribution board connects directly to the power supply and
distributes power to the rest of the boards in the system including the
motherboard. It also distributes power to the disk drives, fan, and CD-ROM. It has
circuity for regulating fan voltage that is temperature dependent as well as
detecting when a fan ceases to spin.
The board also converts standard ATX IDE interface signals into those used by
notebook flexible disk drives and hard disk drives if needed in the system. The
power distribution also distributes various signals between boards such as serial
lines and front panel ID signals that connect between the acquisition board and
the front panel board.
Front Panel Board
The front panel board contains a microcontroller that is powered from 5V. This
particular 5V line comes from a standby rail that is supplied as long as the unit is
connected to AC power. The standby rail powers the microcontoller and some
core circuitry on the front panel board. The remaining circuitry on the front panel
board is powered by the main 5V rail after the supply is turned on by the front
panel microcontroller.
The standby power also supplies a small portion of the motherboard circuitry.
When the motherboard detects that the power switch has been pressed, it will
assert a signal to the microcontroller (via the power distribution board) that tells
the front panel microcontroller to turn the main rails of the power supply on or
off. After the system’s main rails have been powered up, the front panel
microcontroller is then free to turn on front panel LED’s scan the keypad, and
drive control signals to the inverter that cause the display to dim or turn on/off.
The logic analyzer application communicates with the front panel by sending
commands to the acquisition microcontroller, via the 1394 bus, which are then
transmitted serially by the acquisition microcontroller to the front panel
microcontroller. Data is transmitted in the reverse order when the application is
polling the front panel.