Firmware: V2.18 / V--
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5.3.5 System error messages
The system error messages are described in chapter
5.4 Process Image (PI)
The process image for the inputs and outputs is located in the memory area in the controller. The raw values of
all digital and analogue inputs and outputs of the controller are stored there. The operating system, the
firmware, cyclically executes the following three steps:
In the second step, the user's application is executed in the controller from start to end in the programmed
sequence. Therefore, it must be ensured during programming that the individual program modules are
executed quickly. This can be ensured by using state machines.
In CODESYS, the raw values of the analogue inputs are converted into physical values with units by the user
program, the application.
Example:
A room temperature sensor with a 4..20 mA interface and a measuring range of 0 °C..+50 °C
provides a current value of 12 mA. This corresponds to half the measuring range, i.e. 25 °C. The analogue to
digital converter of the analogue input of the controller converts this into the number 19642. If the sensor is
connected to input 7 (terminals 61, 59), the value 19642 is supplied in the process variable AIN7 with the IEC
address IW 48.
Analogue input:
The raw values are read into the PI as a number from the analogue to digital converter ADC
and represent the analogue input value of the physical interface there:
Example: U = 0..10 V [
Analog-IN
] ADU PA = 0..32000
Analogue output:
The program writes a numeric value into the PI, which is converted into a voltage value by
the digital to analogue converter DAC, which is then present at the output of the analogue interface.
Example
: PA = 0…32000 DAU [
Analog Out
] U = 0…10 V
Actively waiting for a message or event and using large, time-consuming program loops in the range of
seconds
must
be avoided, as this will also trigger the watchdog!
