System variables - ESM tasks,  HMI clients and AlarmProgram status

ESM task handling

Available for  AXC F x152, RFC 4072S, RFC 4072R

Programs and program parts are treated as tasks in PLCnext Engineer. Individual tasks are coordinated and processed in the Execution and Synchronization Manager (ESM).

The ESM_DATA system variable can be used to retrieve information on the task handling of the ESM. The ESM_DATA system variable is a system variable organized as a data structure.

Task handling system variables

Note: Since the system variable ESM_DATA is updated by the GLOBALS task, the corresponding IEC 61131-3 system variables were usually not updated when the event task is executed. Therefore, in case of IEC 61131-3 programming the function block GET_EXCEPTION_INFOS must be used to retrieve information which exception was thrown.

System variable	Type	Description
ESM_DATA	ESM_DAT	Data structure
└ ESM_COUNT	USINT	Number of ESMs (one ESM per processor core)
└ ESM_INFOS	ESM_INFO_ARRAY	Information on ESM [1...2] [1]
└ [1]...[2]	ESM_INFO
└ TASK_COUNT	UINT	Number of tasks that have been configured for the ESM
└ TICK_COUNT	UDINT	Always 0 However when a request for this system variable is made from a REST client, the HMI server does not return the value of that system variable (which is always zero), but instead it returns a different value that looks like a tick count.
└ TICK_INTERVAL	UDINT	Always 0
└ TASK_INFOS	TASK_INFO_ARRAY	Information on task [1...16] [1]
└ [1]...[16]	TASK_INFO
└ INTERVAL [2]	LINT	For cyclic tasks: time interval in μs; for acyclic tasks: 0
└ PRIORITY [2]	INT	Priority of task
└ WATCHDOG [2]	LINT	Watchdog time in μs; no watchdog: 0. The watchdog time will be defined for the sum of execution duration and delay time. If the watchdog time is exceeded the watchdog will trigger.
└ LAST_EXEC_DURATION	LINT	Execution duration of the task in the previous cycle in μs (including interruptions by higher priority tasks)
└ MIN_EXEC_DURATION	LINT	Minimum execution duration of the task in μs (including interruptions by higher priority tasks)
└ MAX_EXEC_DURATION	LINT	Maximum execution duration of the task in μs (including interruptions by higher priority tasks)
└ LAST_ACTIVATION_DELAY	LINT	Delay time of the task in the previous cycle in μs (delay occurs if higher priority tasks are pending at the time of task activation)
└ MIN_ACTIVATION_DELAY	LINT	Minimum delay time of the task in μs (delay occurs if higher priority tasks are pending at the time of task activation)
└ MAX_ACTIVATION_DELAY	LINT	Maximum delay time of the task in μs (delay occurs if higher priority tasks are pending at the time of task activation)
└ EXEC_TIME_THRESHOLD [2]	LINT	Threshold value that you can define for the sum of execution duration and delay time
└ EXEC_TIME_THRESHOLD_CNT	UDINT	If the defined EXEC_TIME_THRESHOLD value is exceeded, the value of the EXEC_TIME_THRESHOLD_CNT variable is incremented
└ NAME [2]	STRING	Task name
└ EXCEPTION_COUNT	USINT	Number of exceptions
└ EXCEPTION_INFOS	ESM_EXCEPTION_INFO_ARRAY	Information on exceptions [1...2]
└ [1]...[2]	ESM_EXCEPTION_INFO
└ TYPE_ID	UDINT	ID of the exception 0 = None 1 = ARP exception (see details in SUB_TYPE and SUB_TYPE_ID) 2 = STD exception (see details in SUB_TYPE) 3 = Unknown exception 4 = Signal 5 = Task WatchDog
└ SUB_TYPE	STRING	Subtype of the exception (for example, std::exception, Arp::System::Commons::ArgumentException)
└ SUB_TYPE_ID	UDINT	Provides detailed information for ARP exceptions (if TYPE_ID = 1)0x4000 = PLC exception 0x4001 = PLC division by zero exception 0x4002 = PLC index out of range exception 0x4003 = PLC stack overflow exception 0x4004 = PLC string error exception
└ TASK_NAME	STRING	Name of the task in which the exception occurred
└ PROGRAM_NAME	STRING512	Name of the program instance in which the exception occurred
└ INFORMATION	STRING512	Information on the exception that occurred

1. The AXC F 1152 supports only ESM 1 with 8 tasks.
2. These system variables can be set in the PLCnext Engineer by means of the Tasks and Events editor.

HMI client connections to the PLCnext Engineer web server

Available for  AXC F x152, RFC 4072S, RFC 4072R

An HMI application in PLCnext technology is executed on the PLCnext Engineer embedded HMI server. There are system variables for handling client connections to the HMI web server. These system variables are organized as a data structure:

• The HMI_STATUS (up to 2021.9) and HMI_STATUS2 (from 2022.0 LTS) system variables can be used to retrieve information on the client connections to the HMI web server.
• The HMI_CONTROL system variable can be used to disconnect a client from the HMI web server. 

HMI client connection system variables

System variable	Type	Description
HMI_STATUS (up to 2021.9)	HMI_STATUS_TYPE	Data structure
└ CLIENT_COUNT	UINT	Number of currently existing client connections to the HMI web server
└ CLIENTS	HMI_STATUS_ARRAY	Information on existing client connections
└ [1]...[256]	HMI_STATUS_STRUCT	Client connections 1...256
└ SESSION_ID	STRING	Session ID of the client connection
└ STATION_ID	STRING	Station ID of the client
└ LAST_REQ	LINT	Time of the last request from the client
└ IP_ADDRESS	IP_ADDRESS_ARRAY	IP address of a client in hexadecimal format, e.g. 192.168.1.100 would be [C0].[A8].[01].[64]
└ [0]...[3]	BYTE
HMI_STATUS2 (from 2022.0 LTS)	HMI_STATUS_TYPE	Data structure
└ CLIENT_COUNT	UINT	Number of currently existing client connections to the HMI web server
└ CLIENTS	HMI_STATUS_ARRAY	Information on existing client connections
└ [1]...[256]	HMI_STATUS_STRUCT	Client connections 1...256
└ SESSION_ID	STRING	Session ID of the client connection
└ STATION_ID	STRING	Station ID of the client
└ LAST_REQ	LINT	Time of the last request from the client
└ IP_ADDRESS	IP_ADDRESS_ARRAY	IP address of a client in hexadecimal format, e.g. 192.168.1.100 would be [C0].[A8].[01].[64]
└ [0]...[3]	BYTE
└ STATION_NUM	UINT	Station ID as number
HMI_CONTROL	HMI_CONTROL_TYPE	Data structure
└ CLIENTS	HMI_CONTROL_ARRAY	Information on existing client connections [1 ... 256]
└ [1]...[256]	HMI_CONTROL_STRUCT
└ DISABLE	BOOL	By setting this to true, the selected client is disconnected from the HMI web server

AlarmProgram status 

Available from firmware version 2025.0 and PLCnext Engineer 2025.0

The system variable ALARM_PROGRAM_STATUS belongs to the configurable alarms that can be configured via the PLCnext Engineer software. It displays information on the program instances of the type AlarmProgram.
Further information on configurable alarms can be found in Alarms and PLCnext Engineer help.

Diagnostic information is provided for each AlarmProgram instance in the ALARM_PROGRAM_STATUS variable that appears in the Data List of PLCnext Engineer. This information can be used to determine the amount of time an ESM task cycle spends evaluating alarm expressions versus performing other task logic, such as evaluating IEC 61131-3 control programs. These values can help to configure a real-time schedule, for example, by adjusting the task interval or number of alarm expressions in the project.

System variable	Type	Description
ALARM_PROGRAM_STATUS	ALARM_PROGRAM_STATUS_TYPE	Data structure
└ ALARM_PROGRAM_INFO_ARRAY	ARRAY[1..16] OF ALARM_PROGRAM_INFO_TYPE	Each of the 16 elements of the array contains diagnostic information for one AlarmProgram instance.   Note: Currently, only one program instance is supported by PLCnext Engineer. The information will appear in array slot 1. The remaining 15 slots will contain empty or zero values in their fields.
└ALARM_PROGRAM_INFO_TYPE	STRUCT	The fields in the ALARM_PROGRAM_INFO_TYPE struct contain duration values that convey how long the alarm program spent processing the alarm expressions. The duration values are displayed in microseconds.
└ NAME	STRING[512]	AlarmProgram name The canonical name of the AlarmProgram instance, for example Arp.Services.AlarmServer/MyAlarmProgram
└ LAST_EXEC_DURATION	LINT	Last execution duration The number of microseconds spent processing alarm expressions during the last ESM task cycle.
└ MIN_EXEC_DURATION	LINT	Minimum execution duration The minimum duration (in microseconds) for processing alarm expressions in all task cycles since the device was started.
└ MAX_EXEC_DURATION	LINT	Maximum execution duration The maximum duration (in microseconds) for processing alarm expressions in all task cycles since the device was started.

 

• Published/reviewed: 2025-06-06  ✿  Revision 080 •