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Device-Channels and Device-Channel Arrays

As the name implies, a device-channel (DEVCHAN) is a combination of a device and a channel. It is represented internally as a DEVCHAN structure.

This structure combines the fields of a DEV structure representing the device with a field representing the channel number.

Syntax

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STRUCTURE DEVCHAN
{
    DEV Device
    INTEGER Channel
}

The first component of a device-channel pair represents the device number, port, and system can be specified as either a single device number, a constant DEV structure or as a D:P:S specification (see explanation under Devices). Each device specified in a device-channel pair should be defined in the DEFINE_DEVICE section.

Channels are expressed as integer constants. A DEVCHAN is declared in the DEFINE_VARIABLE or DEFINE_CONSTANT section.

For example, "[128, 1]", "[ CONSTANTDPS, 9]" and "[128:1:0, 5]" are all valid representations of device-channel pairs.

A DEVCHAN enclosed within square brackets implies an evaluation, whereas a DEVCHAN enclosed within curly braces does not, as illustrated below:

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DEFINE_VARIABLE
DEVCHAN dc1 = {128:1:0, 1}
DEVCHAN dcset[] = { {128:1:0, 1}, {128:1:0, 2}, {128:1:0, 3} }

DEFINE_PROGRAM

If ( [dc1] || [128:1:0, 2] ) // evaluation of 2 devchans
[dc1] = 3    // feedback

dc1 = {129:1:0, 2}   // assigns a new value to dc1
[dc1] = {129:1:0, 2}   // Syntax Error!

An array of DEVCHANs, a DEVCHAN array, is declared in the DEFINE_VARIABLE or DEFINE_CONSTANT section in one of two ways:

  1. Declare a DEVCHAN array whose maximum length is determined by the number of elements in the initialization array on the right-hand side, as shown below:

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    DEVCHAN DCSName[]= {{Dev1,Chan1}, {Dev2,Chan2}, ...}

  2. Use MAXLEN to specify the maximum length of the array, as shown below:

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    DEVCHAN DCSName[MAXLEN] = {{Dev1,Chan1}, {Dev2,Chan2}, ...}

In either case, the number of elements in the initialization array determines the effective length of the array. That value can be determined at run-time by calling LENGTH_ARRAY. The maximum length available for a DEVCHAN[] array can be determined by calling MAX_LENGTH_ARRAY.

The individual elements of a DEVCHAN array can be referenced by their defined names (Dev1, Chan1, Dev2, Chan2, etc.) or alternatively, by using array notation with the device-channel array name.

For example, the third element in the device-channel array, MyDCSet would be referenced by MyDCSet[3].

Furthermore, since a DEVCHAN array is an array of DEVCHAN structures, DEVCHAN members can be referenced using the dot Operator notation such as MyDCSet[3].Device or MyDCSet[1].Channel.

A DEVCHAN array can be used anywhere a [Device, Channel] specification is required with the result of providing a range of targets for the command or instruction where it is used. This implies an alternate form for the following commands:

  • Button[(DEVCHAN)]
  • DO_PUSH[(DEVCHAN)]
  • DO_RELEASE[(DEVCHAN)]
  • OFF[(DEVCHAN)]
  • ON[(DEVCHAN)]
  • PULSE[(DEVCHAN)]
  • PUSH[(DEVCHAN)]
  • RELEASE[(DEVCHAN)]
  • TO[(DEVCHAN)]

The index of the last member of the array for which an event notification was triggered can be determined by calling Get_Last(MyDCSet). This is useful for determining which device and channel in an array is referenced to in a particular notification message.

See Also