Bradley Smoker PLC-5 user manual Suggested Action, Msg

Troubleshooting F-11

This	Executes These Actions During Prescan:
Instruction:
FOR	Ladder instructions within the FOR/NXT loop are prescanned.
MSG	If the SFC startover bit is cleared and the CO bit is cleared, then all
	non-user configuration bits 15, 14, 13, 12, 10, and 9 are cleared in both
	the INT and MG file types. The MG file type also clears bits 11, 7, 6, 5, 4,
	2, 1, and 0.
ONS	The programmed bit address of the instruction is set to inhibit false
	triggering when the first run-mode scan begins.
OSF	The programmed bit address of the instruction is cleared to inhibit false
	triggering when the first run-mode scan begins. The output bit is also
OSR
	cleared.
PID	For PD file type, the INI bit is cleared.
	INT file type clears status bits 8, 9, and 10 (deadband, upper, and lower
	output alarm). The error register from the previous scan is set to 32767,
	which indicates that the setpoint and ER bits from previous scans have
	not yet been initialized). The Integral Accumulator and Derivative Error
	bits are cleared.
SQL	The EN bit is set to prevent a false increment of the table pointer when
	the first run-mode scan occurs.
SQO
TOF	The TT, TC, TE, and TO bits are cleared and the ACC = preset.
DTR (1)	The reference value is updated (regardless of the rung condition).

(1)The DTR instruction operates in this manner during a normal scan as well.

Suggested Action

To avoid unexpected operation that may result from these prescan activities, follow these guidelines:

•Do not use indexed or indirect addressing with the instructions listed in the above table.

•If you must use indexed or indirect addressing, use the first scan bit (S:1/15) to pre-initialize all of the other used variables.

•If using indirect addressing with any ladder instructions, do not use the data variable holding the indirect address for multiple functions.

Publication 1785-UM012D-EN-P - July 2005