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Lazy Line Transitions

Last Modified: September 15, 2017

When a task-based route gets created and released, it does not necessarily go away. The hardware resources associated with the route are released, but the configuration might remain so that glitches are minimized.

By default, all tristate buffers associated with I/O connector terminals are disabled. When a task-based route with a destination on the I/O connector is released, the tristate buffer associated with the I/O connector terminal is not disabled. This means that even though the route was released, glitches are minimized on the destination terminal on the I/O connector. If you do not want this behavior, you can disable the tristate buffer associated with the I/O terminal with the Tri-State Output Terminal function/VI. Or, if you initially created the route by exporting a signal with the Export Signal function/VI, you can also disable the tristate buffer by calling the Export Signal function/VI with the same signal name but with an empty string as the output terminal. Putting the terminal back into a tristate mode is necessary if an external signal must be connected to the I/O terminal. If the terminal is not tristated first, double driving the terminal damages the hardware.

All other connectors, such as the RTSI connector, use a different rule. When the task-based route associated with the RTSI connector is released, the tristate buffer associated with the RTSI terminal is disabled. The RTSI bus is a public bus that is shared by multiple devices. All drivers using the RTSI bus assume that all devices on the bus are tristated. The I/O connector is different because you have full control of it. You must keep track of which terminals are tristated or being driven by internal or external signals.

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