Discrete Input function block execution

I/O selection

When you configure the Discrete Input function block, you select the I/O channel associated with the discrete measurement by configuring the Device Signal Tag (DST) of the IO_IN parameter. You select the Device Tag and the parameter the Discrete Input block accesses on that channel.

When you select Discrete Input Channel for the channel type, the only selectable channel parameter is:

FIELD_VAL_D — The last value reported by the card and the current status of the channel.

You configure contact debounce filtering during I/O configuration.

Simulation

To support testing, you can enable simulation. This allows the measurement value and status to be supplied manually or from another block.

When the block is downloaded to a controller, enabling SIMULATE_D sets the Simulate Active bit in the BLOCK_ERR parameter. When the block is downloaded to a workstation the Simulate Active bit is not set.

During configuration, decide whether you want to enter the simulated value/status manually during operation or use a value/status from another block for the simulated value/status.

When the value is entered manually:

The operator first enables simulation by selecting the SIMULATE_D parameter and setting the Simulate Enabled check box in the Simulate Enabled/Disabled field.
If SIMULATE_IN_D is not connected (status = Bad: NotConnected), the operator enters the value to be used in the SIMULATE_D parameter Simulate Value field. In online operation, the operator can enter a simulated status value in the Simulate Status field.

Note

Make sure SIMULATE_IN_D is not connected if you want to enter the value or status manually. When SIMULATE_IN_D is connected, the value from the SIMULATE_IN_D Value field is used as the simulated value.

When the value/status from another block is used:

During configuration, connect SIMULATE_IN_D to the desired block output or parameter. Do not enter a value in the Simulate Value field of the SIMULATE_IN_D input; the block uses the connected value automatically.
During operation, the operator enables simulation by selecting the SIMULATE_D parameter and setting the Simulate Enabled check box in the Simulate Enabled/Disabled field.

Note

Do not enter a value for the SIMULATE_IN_D parameter. If you do and the status of SIMULATE_IN_D is not Bad: NotConnected, the manually entered value for SIMULATE_IN_D overrides any value you enter in SIMULATE_D.

When SIMULATE_D is not enabled, the hardware value becomes the FIELD_VAL_D parameter value in the block. When SIMULATE_D is enabled, the value and status of the SIMULATE_IN_D parameter become the value and status of FIELD_VAL_D.

Field value processing

You can configure the Invert I/O option (IO_OPTS) to process FIELD_VAL_D.

Invert

The output of the Invert processor is PV_D. This value goes to the mode switch where it becomes OUT_D when the mode is Auto. OUT_D is tested for an alarm state. You might select this option when the field contact is normally closed, so an open contact or a broken wire represents the active state of the condition being sensed.

PV filter

Filtering in a Discrete Input function block is performed with on and off delays. FIELD_VAL_D must be on (or off) for PV_FTIME without changing before the block passes a change to PV_D.

Note

You can set the I/O option in Manual or Out of Service mode only.