GE Mark VIe System Manual page 39

In a dual control system, the application logic in each controller tries to produce the same results. After many iterations of
running the application, it is possible for the internal data values to differ due to mathematical round off, and different past
history (power-up). To converge this data, the internal data (state) variables are taken from the designated controller and
transmitted to the non-designated controller for its use. This is known as state exchange.
State variables are any internal variables not immediately derived from input or control constants. Any variable that is used
prior to being re-calculated is an internal state variable.
This principle can be displayed in the following two equations:
A = B+C
C = 3 x D
Assume B and D are inputs and A and C are intermediate values. Since C is used prior to being calculated, the value of C
during the previous scan retains some state information. Therefore, C is a state variable that must be updated in the
non-designated controller if both controllers are to remain synchronized.
In the Mark VIe controller, Boolean state variables are updated on every control frame. The analog state variable updates are
multiplexed. A subset of analog state variables is updated every control frame. The controller rolls through each subset until
all state variables are transmitted.
Control System Overview GEH-6721_Vol_I_BP System Guide 39
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