Indigo system


GPIsUsing GPIs is one control option offered by Crystal Vision, and is available for most products in the Indigo range.

Board edge control is not currently available for the Vision frame system.

GPIs appeal to people who want their control as simple and robust as possible. This control interface is as simple as it gets: the line is either high or low, with no protocol and no software.

So how does GPI operation work?


Using GPI control

GPI stands for General Purpose Interface. There are two types of GPI connections: inputs and outputs. Some Crystal Vision boards offer just GPI inputs, others just GPI outputs while many offer both.

A GPI input is a circuit to sense the voltage on a wire. GPI inputs are used when an automation system wants to trigger Crystal Vision equipment to do something at a specific time generally to recall a preset. The automation system changes the state of an electrical switch (usually a relay or transistor) which is connected to the GPI wire, and the Crystal Vision equipment senses the change in voltage (either high to low, or low to high) and performs the required action.

For example, on the SYNNER 310 synchroniser there are four GPI inputs that set the preset being recalled. If these four GPI inputs are set to high, high, high, high you would recall preset one; to recall preset two you would set them to high, high, high, low and so on.

A GPI output is a switch to change the voltage on a wire. GPI outputs are used to indicate a change in state, such as an error being detected. The Crystal Vision product turns a transistor on or off, which typically either illuminates a light or feeds into a fault monitoring system.

The GPI inputs can be either 'latching' where they are intended for use with pulse signals (the switch is turned on for a short period to trigger the action) or 'momentary' where they are intended for use with level signals (the switch is turned on permanently to trigger the action).

It is also possible to choose whether the GPI is asserted (i.e. in its active state) when the switch is on (active low) or when the switch is off (active high).

The functionality of the GPI inputs is generally fixed on most Crystal Vision boards. The functionality of the GPI outputs is also relatively fixed, although for error GPIs it is usually possible to select from a list the errors you wish to monitor. Safe Switch is an example of a board where the bi-directional GPIs offer more configurability freedom.

The boards' GPI inputs and outputs are connected to external equipment via the frame. Each frame slot has six GPI connections which go to 26-way D-Type connectors on the rear of the frame there are four of these D-Types available on a 2U frame and two on the 1U frames and desk top boxes. From each frame slot, four GPI connections go to one D-Type and two to another. Cabling from the D-Types will then connect the GPI signal to any external equipment.

GPI is such a simple signal that it allows you to perform simple functions without a processor meaning that GPI capability is also available on the non-remote controllable products.


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