Siemens SINUMERIK 840Di Function Manual page 1235

2.7.6 Response to NCK failure
General
During cyclic operation, the PLC basic program continuously monitors NCK availability by
polling the sign-of-life character. If the NCK is no longer reacting, then the NCK PLC
interface is neutralized and IS NCK CPU ready in signals from NC group (DB 10.DBX 104.7)
is reset. The signals sent by the NCK to the PLC are initialized with default settings.
The PLC itself remains active so that it can continue to control machine functions. However,
it remains the responsibility of the user program to set the machine to a safe state.
NCK -> PLC signals
The signals sent by the NCK to the PLC are divided into the following groups:
• Status signals from the NCK, channels, axes and spindles
• Modification signals of the auxiliary functions
• Values of the auxiliary functions
• Values of the G functions
Status signals:
The status signals from the NCK, channels, axes, and spindles are reset.
Auxiliary-function modification signals:
Auxiliary-function modification signals are also reset.
Auxiliary-function values:
Auxiliary-function values are retained so that it is possible to trace the last functions triggered
by the NCK.
G-function values:
G function values are reset (i.e. initialized with the value 0).
PLC -> NCK signals
The signals sent by the PLC to the NCK are divided into control signals and tasks that are
transferred by FCs to the NCK.
Control signals:
The control signals from the PLC to the NCK are frozen; cyclic updating by the basic
program is suspended.
PLC Basic Program Solution Line (P3 sl)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
2.7 Structure and functions of the basic program
Detailed Description
2-41