Theory of operation
Main board
The Main board provides most of the interconnections to the other boards,
modules, and secondary power supplies. The Main board houses the PLD, voltage
monitor ADC, LTC channels, and the GPIO and Expansion ports.
PLD
The Main board contains the PLD, which has the logic for the Channel Control
function. This PLD monitors the left-hand front panel buttons and the fault
inputs from the modules to control the state of the ECO. The PLD also drives the
per-channel fault LEDs. The PLD also restores settings from a small EEPROM
on power up
so that the primary function of the ECO can be functional before the
processor boots.
Wa tchdog timer. The Main board PLD has a watchdog timer. If the processor
stops communicating with the PLD for 20 minutes, then the PLD will reset the
processor. The CPU reset can also be achieved by enabling the left panel (Channel
Contro
l system), and then pressing and holding both the ENABLE and RESET
buttons for 6 seconds.
NOTE. A CPU reset has no effect on the state or operation of the ECO relays, so it
is safe to perform the reset during normal instrument operation.
Reprogramming. The Main board PLD can be reprogrammed by the processor
via a JTAG interface. A separate JTAG interface is multiplexed to each Cha nnel
module so that the Processor can update the PLDs on those modules.
Voltage monitor ADC
The Main board houses the voltage monitor ADC, which is driven by a system
of multiplexers that allow a variety of voltages to be m easured. Each Channel
module has a multiplexer to allow all power supply, peak detector and threshold
voltages to be selected one at a time. The one selected signal from each Channel
m
odule, and selected signals from the Main board are again multiplexed to
eventually drive one input to an ADC. The software and processor hardware step
through all of the possible inputs to the ADC and measure each one. The results
are displayed in the Diagnostic menu. This simple voltage monitor can give a
significant view into the health of the instrument.
LTC channels
The LTC channels on the Main board are similar to the channels on the Channel
modules. The 15-pin, high-density “VGA” style DSUBs connect the differential
LTC inputs from the sync sources, and the output DSUB provides the selected
source as an output. The pin-out of the DSUBs are compatible with the LTC
outputs on the SPG8000 and GPS7 module of the TG8000, which allows the
instruments to connect together with a standard cable.
2–4 ECO8000 Series Service Manual
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