Siemens SINUMERIK 840D sl Function Manual page 42

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Detailed description

2.2 Functions

The maximum number of simultaneously writable output variables is adjustable via:

MD28150 $MC_MM_NUM_VDIVAR_ELEMENTS (number of elements for writing PLC

A WORD is to be transferred from the PLC to the NC.

The position offset within the NCK input (PLC output area) should be the fourth byte. The

position offset must be a whole-number multiple of the data width.

• Writing from PLC:

Program code (extract)

Enable :=M10.0,

Funct :=B#16#4,

S7Var :=P#M 104.0 WORD1,

Error :=M10.1,

ErrCode :=MW12);

If a read/write access is made from the NCK to a variable in the dualport RAM, the

conversion is performed twice. It is impossible to prevent differences between read and

written values because the data are stored in both formats.

Bypassing the problem by means of comparison on "EPSILON" (minor deviation)

Program code

DEF REAL DBR

DEF REAL EPSILON = 0.00001

$A_DBR[0]=145.145

DBR=$A_DBR[0]

IF ( ABS(DBR/145.145-1.0) < EPSILON ) GOTOF ENDE

MSG ( "error" )

;if TRUE, then FC21 active

Basic logic functions: Various NC/PLC interface signals and functions (A2)

Function Manual, 11/2006, 6FC5397-0BP10-2BA0

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