Bradley Smoker PLC-5 user manual Increased Program Scan Time, Force Privileges

13-4Programming Considerations

For BTR instructions using non-configured data tables, the .DN bit indicates when data is valid in the BTR data file. When you configure files in the extended force configuration table, the .DN bit indicates that the data is in the BTR data buffer. The BTR data is not forced and moved into the BTR data file until the next housekeeping period. Delay using the BTR data until the scan after the .DN bit is set.

For BTW instructions using non-configured data tables, the data that is in the BTW data file when the block-transfer is enabled is transferred. When you configure files in the extended force configuration table, the data that in the BTW data buffer when the block-transfer is enabled is transferred. Any new data in the BTW data file is not forced or moved into the BTW data buffer until the next housekeeping period. Delay enabling the BTW instruction until the scan after the BTW data file is updated.

Increased Program Scan Time

When you use the extended forcing feature, program scan time increases proportionately to the number of words you configure in the extended force configuration table. The amount of increase depends on whether you enable or disable forces. Typical increases in program scan time when you configure data table files in the extended force configuration table are:

When Forces are	Scan Time Increases by this Much
	Per Word	Per 1000 Words
enabled	0.003 ms	3.0 ms
disabled	0.0015 ms	1.5 ms

I/O Force Privileges

The I/O forcing privilege lets you enable, disable, or clear all forces in the controller. This privilege now includes extended forcing.

Extended forcing reads force data in a read data file; extended forcing writes force output data, leaving the write data file in its original state.

IMPORTANT

Forces are held by the controller (and not the personal computer). Forces remain even if the personal computer is disconnected.

Publication 1785-UM012D-EN-P - July 2005