X-ray On, X-ray Disable
Digital Logic Signal Levels
Logic signals that are connected from one PCB assembly to another, for example, will assume TTL logic levels, i.e., logical low is
≤0.8V, and logical high is ≥2.0V (in most cases, ≥4.0V.)
Critical logic signals will be transmitted from one board to another using a pull-up resistor on the destination board, and typically
none on the originating board, and will be so configured that in the event of an open-circuited connection, the high state input at
the destination board will result in a safe condition, e.g., if the FAULT signal originating on the Generator Driver PCB is active
high, and is configured to prevent X-ray generation at the destination HV Supply Regulator PCB, then absence of a connection
will cause the destination PCB to fail safe and prevent generation of X-rays. Alternatively, absence of a connection from the
collector of the transistor on the Filament Driver PCB which generates the GND_INTEG* signal, active low, will cause the pull-up
resistor on the destination HV Supply Regulator PCB to pull up this line to a logic high level and disable X-ray production.
Specific examples of this rule are tabulated below. All PCBs are listed here even though some are not described within this
section.
9
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