Direct Plc I/Os, Addressable From The Nc - Siemens SINUMERIK 840D sl Function Manual

1.2.5

Direct PLC I/Os, addressable from the NC

Introduction
The fast data channel between the NCK and PLC I/Os is processed directly and, therefore,
quickly by the PLC operating system.
There is no provision for control of the PLC basic and user programs. It is not advisable for
the NCK and the PLC to attempt to access the same PLC I/Os simultaneously, as this can
result in faults.
System variables
For access purposes, the NC uses system variables associated with part programs and
synchronized actions.
For reading from PLC:
$A_PBB_IN[n]
$A_PBW_IN[n]
$A_PBD_IN[n]
$A_PBR_IN[n]
Reading from the part program causes a preprocessing stop.
For writing to PLC:
$A_PBB_OUT[n]
$A_PBW_OUT[n]
$A_PBD_OUT[n]
$A_PBR_OUT[n]
The output data can also be read from the part program and synchronized actions. Reading
from the part program causes an automatic preprocessing stop (to achieve synchronization
with the real-time context).
Extended Functions
Function Manual, 09/2009, 6FC5397-1BP20-0BA0
; Read byte (8-bit)
; Read word (16-bit)
; Read data word (32-bit)
; Read real (32-bit float)
n Byte offset within the PLC input area
; Write byte (8-bit)
; Write word (16-bit)
; Write data word (32-bit)
; Write real (32-bit float)
n Byte offset within the PLC output area
A4: Digital and analog NCK I/Os
1.2 NCK I/O via PLC
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