Bradley Smoker PLC-5 user manual Do not use BTR data tables files to store

Programming Considerations 13-3

The 1771 read command type of the CIO instruction operates in the same manner as the BTR instruction; the 1771 write command type of the CIO instruction operates in the same manner as the BTW instruction. For simplicity, the following descriptions and examples of extended forcing refer to the BTR instruction (for BTR and 1771 read command type of CIO instructions) and the BTW instruction (for BTW and 1771 write command type of CIO instructions).

You program block-transfer instructions in the same manner, regardless of whether you configure the data file in the extended for configuration table. The following figure shows how block-transfer data table files are updated during housekeeping.

BTR instruction execution

BTR	BTR
Data File	Data Buffer

each housekeeping period

BTR Module

BTW

Data File

BTW Data Buffer

BTW Module

BTW instruction execution

When you use extended forcing, you affect the way your programmable controller system operates, Before you begin to use this forcing feature, read this entire section to understand the effects.

Any block-transfers or data table locations included in

ATTENTION	the extended force configuration table will be affected
	regardless of whether forces are enabled.

	Do not use BTR data tables files to store
ATTENTION
	non-block-transfer data. All non-block-transfer data
	that you include in the extended force configuration
	table as read data will be forced to zero during
	housekeeping at the end of each program scan. If your
	ladder program expects values other than zero for this
	data, unpredictable machine operation could result.

Publication 1785-UM012D-EN-P - July 2005