I/O hooks are the things that link [JSup tag|tags] with remote device items.

An I/O hook can be added to a [JSup tag|tag] by clicking Add button of the I/O hook table in the [JSup Tag dialog|Tag dialog].

The I/O hook dialog lets the user to:

• associate the I/O hook with a [JSup Channels|channel];
• define the item the I/O hook will be linked to within the remote device;
• specify some [JSup Drivers|driver] dependent information (if any);
• make the I/O hook to be read or write only.
• specify some [JSup Tag type|tag type] dependant configuration.

I/O hook channel

An I/O hook belongs to a [JSup Channels|channel] that control when and how data are read/written from/to the remote device.

An I/O hook inherits some properties from it:

• the channel item prefix (if any) that will be prefixed to the I/O hook item to complete it.
• the remote device and the way it is read/written (timed/triggered, written on tag change).
• the [JSup Drivers|driver] used.

Item

The item defines the address within the remote device to be read/written by the I/O hook.
The [JSup Channels|channel] can provide a prefix the all the items of the I/O hook that belong to it.

The format of this item is [JSup Drivers|driver] dependent.

Tag array element items

Items for I/O hooks of a [JSup Tag arrays|tag array] elements are calculated as a [JSup Math code|math expression] where indexes of the element are provided in i, j and k variables (for a single dimensional array only i, for two dimension array i and j only).
For example: "%mw"+(1000+i)

Programmatically calculated items

See also:

• [JavaCode function provided IOHooks|JavaCode function provided I/O Hooks]

Programmatically calculated items can be provided to I/O hooks, expecially useful for [JSup Structured tags|structured tag members] o [JSup Tag arrays|array] elements (see below for array special case).
If the item starts with the prefix "::=" the rest of the item is interpreted with the following special place holders that let Java method or JavaCodeFunction to be called to provide the item:

%JavaCodeFunctionForTag javaCodeFunctionName%
Will be replaced with the value of the given [JavaCode functions], that must return a String value and must have a single [TagRef] parameter (a reference to the tag instance, or the array element). For example:
::=%JavaCodeFunctionForTag ifEntryOID%

Example of ifEntryOID( TagRef tag ) [JavaCode functions

JavaCode function]

TagRef structTag = tag.getStructTag();
String ifEntryChild = ((TagStructMemberRef)tag).getMemberDefinition().getProperty( "ifEntryChild" );
if( ifEntryChild == null ) ifEntryChild = "999";
return "1.3.6.1.2.1.2.2.1."
	+ifEntryChild+"."
	+structTag.getProperty( "ifIndex", "999" );

%JavaCodeFunctionForTagAndChanneljavaCodeFunctionName%
Will be replaced with the value of the given [JavaCode functions], that must return a String value and must have two parameters:

1. [TagRef] a reference to the tag instance, or the array element.
2. [ChannelInfo] information about the [JSup Channels|channel] the item will be provided to.

%callForTag full.package.class.methodName%
Will be replaced with the value of the given static Java functions, that must return a String value and must have a single [TagRef] parameter, where a reference to the tag instance (or array element). This can be useful to invoke library class methods defined in JavaCode imports (see [JSup Application properties])

To provide programmatically calculated items to an [JSup Tag arrays|array] element provide, as item [JSup Math code|math expression], a single double quoted string constant that starts with "::=", for example:
"::=%JavaCodeFunctionForTagAndChannel addressForDeviceTime%"

Driver dependant info

Some driver require or allow to enter some extra configuration data.
Press the button (if enabled) to enter such data.

Read/write only

It's a good practice to specify if an I/O hook is to be only read or written.

A read only I/O hook that belongs to a [JSup Channels|channel] that is both read and written will never be written to the remote device. It will be simply skipped when the [JSup Channels|channel] content is written to the remote device.

A write only I/O hook will be never read from the remote device even if the [JSup Channels|channel] is configured for read operations.

It's a good practice to specify if an I/O hook is to be only read or written, even if the [JSup Channels|channel] is configured only for read or write because:

• it will be useful to understand the way the [JSup application|application] communicates when looking the [JSup IOHook list|I/O hook list];
• it will save the [JSup application|application] from possible future errors, if the [JSup Channels|channel] configuration changes.

Type dependent config

Boolean

A [JSup boolean tags|boolean tag] I/O hook can be reversed so when tag value of true corresponds to a 0 in the remote device, and a false tag value corresponds to a 1 in the remote device.

Numeric

A [JSup numeric tags|numeric tag] I/O hook can define a min/max raw range to scale the [JSup tag|tag] value within its EU min/max range. The EU min/max range can be defined using the [JSup Using tag properties|tag properties] or defining it within the [JSup Tag classes|tag class]. When no min (or max) is given from tag [JSup Using tag properties|properties] the Java corresponding type minimum (or maximum) value is used (See [http://java.sun.com/javase/6/docs/api/java/lang/Byte.html#MIN_VALUE|Byte], [http://java.sun.com/javase/6/docs/api/java/lang/Short.html#MIN_VALUE|Short], [http://java.sun.com/javase/6/docs/api/java/lang/Integer.html#MIN_VALUE|Integer], [http://java.sun.com/javase/6/docs/api/java/lang/Long.html#MIN_VALUE|Long], [http://java.sun.com/javase/6/docs/api/java/lang/Float.html#MAX_VALUE|Float] and [http://java.sun.com/javase/6/docs/api/java/lang/Double.html#MAX_VALUE|Double]).
Please note that is always better to define the raw value min-max range withing [JSup Tag classes|tag class]. Use the I/O hook specific raw range only as exception (for example for a tag with multiple I/O hooks that need different scaling).

With a linear conversion (no square root) for conversion formulas are
    vr = (ve - mine) * ((maxr - minr) / (maxe - mine)) + minr

    ve = (vr - minr) * ((maxe - mine) / (maxr - minr)) + mine
Where the subscript r means raw (remote device side), and e means engineering (JSup side)

When the square root flag the following formula is used to convert the raw numeric value (read from the remote device) into the tag value:

Where the subscript r means raw (remote device side), and e means engineering (JSup side).

And the formula to convert the tag value into the raw value to be written to the remote device is:

The raw value sign can inverted specifying a min raw greater than the max raw. In this case, to perform calculations, the min/max raw values are swaped in the natural order, and the raw value sign is inverted.

Multiple I/O

A [JSup tag|tag] can have more than one I/O hook. In this case the I/O hooks of a [JSup tag|tag] should belong to different [JSup Channels|channels] that should be triggered read/written: the trigger should be handled by some [JavaCode].

I/O hook list

The complete list of I/O hooks defined in the [JSup application|application] can be viewed with the [JSup IOHook list|I/O hook list] window.