Staubli CS8C, Instruction Manual

Page: 97 / 248

CS8C © Stäubli 2009 –
D28070504A
97 / 248
Chapter 5 - Integration
Overrun
error
If execution of a
PLC
cycle takes longer than the specified cycle time, the current cycle ends normally, and then
the following
PLC
cycle starts immediately. An
Overrun
error is generated (on the
dOverrun
digital output by
default) to enable a reaction to the
PLC
or
VAL3
program.
The
dOverrun
digital output thus shows during each
PLC
cycle whether the previous cycle was carried out within
the specified time lapse or not. The name of the output can be changed (see"Configuration"). The value
1
shows
the
Overrun
error.
Input/Output error
If an Input/Output reading / writing error is detected, a
RwError
error is generated by the default
dRwError
digital
output to enable a reaction by the
PLC
or
VAL3
program. The name of the output can be changed
(see"Configuration").
Interaction with the
VAL3
program
When the
PLC
cycle time is not null:
Execution of the
PLC
program takes priority over the
VAL3
program. The
VAL3
program is only executed once
the
PLC
program is waiting, between two
PLC
cycles.
Execution of a
VAL3
program can be interrupted at any time by a repeat of a
PLC
cycle. If synchronization is
required between the
PLC
and the
VAL3
, it has to be programmed using the Inputs/Outputs.
When the
PLC
cycle time is null:
Execution of the
VAL3
program takes priority over the
PLC
program. The
PLC
program is only executed once the
VAL3
program is waiting, between two
VAL3
cycles.
Inputs/Outputs are refreshed with each
PLC
cycle, each
VAL3
synchronous cycle and each
VAL3
asynchronous
cycle.
PLC
utility for the
MCP
The main menu of the
CS8C
includes a
"PLC"
utility that displays the main characteristics of the
PLC
program
being executed:
•
Requested
PLC
cycle time (as defined in the
PLC
programming environment)
•
Measurement of the execution period for the last
PLC
cycle (this period includes the execution time for
the critical system tasks)
•
Maximum execution time measured for the
PLC
cycles since the previous
PLC
start
• TCP
port for communication with the
PLC
programming environment
CPU
load
The ratio between the execution period for the previous
PLC
cycle and the requested
PLC
cycle time gives the
current
CPU
load for the
PLC
program. The ratio between the maximum execution period for the
PLC
cycle and
the requested
PLC
cycle time gives the maximum
CPU
load for the
PLC
program.
The unused
CPU
load is allocated as a priority to the
VAL3
, and then to non-critical system tasks (screen
refreshing,
Ethernet
communication). As a rough guide, it is necessary to leave about
30%
of the
CPU
load to
obtain correct execution of a
VAL3
program and the system. For a very simple
VAL3
program, we can let the
PLC
use
90%
of the
CPU
load. For a complex
VAL3
program, the
PLC
program should not exceed
50%
of the
CPU
load.
CAUTION:
If the delay between two
PLC
cycles is not long enough, execution of the
VAL3
program can
be slowed down considerably. It is then necessary to increase the
PLC
cycle time to leave
more time for the
VAL3
, or to specify a null cycle time for the
PLC
(see "
CPU
load").