RTC

The function block RTC (Real Time Clock) can be used to realize an internal software clock in the TwinCAT PLC. The clock must be initialized with a starting date and time. After the initialization the time and date are updated with each call of the function block. A CPU system clock is used to calculate the current time and date. The function block should be called in every PLC cycle, so that the current time can be calculated. The current date and time are available in the usual DATE_AND_TIME (DT) format at the function block's output. Multiple instances of the RTC function block can be created within one PLC program.

	Deviation of the RTC time from a reference time The way the system works means that the RTC time can differ from the reference time. The deviation depends on the PLC's cycle time, the value of the basic system ticks, and on the hardware being used. In order to avoid larger deviations the RTC instance should be synchronized cyclically (e.g. with a radio clock or with the local Windows system time). The local Windows system time you can be synchronized with a reference time via the SNTP protocol.

Inputs

VAR_INPUT
   EN  : BOOL;
   PDT : DATE_AND_TIME;
END_VAR

Name	Type	Description
EN	BOOL	The RTC_EX2 function block is re-initialized with a specified date, time and millisecond by a rising edge at this input.
PDT	DATE_AND_TIME	(Preset Date and Time) The initialization values for the function block's date and time. A rising edge at the EN input will cause the function block to adopt this value.

Outputs

VAR_OUTPUT
   Q    : BOOL;
   CDT  : DATE_AND_TIME;
END_VAR

Name	Type	Description
Q	BOOL	This output is set if the function block has been initialized at least once. If the output is set, the values for the date, time and milliseconds at the PDT output are valid.
CDT	TIMESTRUCT	Current Date and Time of the RTC_EX2 instance. The CDT output is only updated when the function block is called. For this reason, instances of the function block should be called once in each PLC cycle.

Example:

See: Example: Software clocks (RTC, RTC_EX, RTC_EX2).

Requirements

Development environment	Target platform	PLC libraries to be integrated (category group)
TwinCAT v3.1.0	PC or CX (x86, x64, ARM)	Tc2_Utilities (System)