Distributed Clock settings

“DC” tab

The DC/Advanced Settings tab can modify the behavior of the EL1202-0100 in association with the local DC.

General

Interrupt SYNC0 or SYNC1 is triggered when the time in the DC matches the specified value for the relevant SYNC (“NextSync0Puls” or “NextSync1Puls”). “NextSync0Puls” is also made available as process data, the “NextLatchTime”. The EtherCAT slave controller (ESC) in the terminal has the job of handling these DC operations.

Default setting

The cyclic read of the inputs is triggered by the SYNC0 pulse (interrupt) from the DC in the EL1202-0100. The standard arrangement is for the reading cycle time of the EtherCAT master to be set to the PLC cycle time being used, and therefore to the EtherCAT cycle time.
(Fig. Advanced Distributed Clock (DC) settings, EL1202-0100 terminal: 4000µs = 4 ms, as TwinCAT is in configuration mode.  

Use in the EL1202-0100

On starting the EtherCAT system, the first specified value is set by the EtherCAT master to “Current DC time” + SYNC0 Cycle Time + SYNC0 Shift Time (see Fig. Advanced Distributed Clock (DC) settings, EL1202-0100 terminal). The EtherCAT slave controller now continues to check its local DC clock for agreement with the specified value. If the specified value matches the DC time, SYNC0 is triggered, which in turn causes reading of the inputs to begin immediately. The specified value is then counted on: “new specified value” = “old specified value” + SYNC0 cycle time. This process now continues from here. The EtherCAT master continuously adjusts all the DC clocks in the EtherCAT system. Further information will be found under www.beckhoff.de

Distributed Clock settings

• Cyclic mode/enable
  Switches the DC on.
• Operating mode
  Only DC latch is possible.
• SYNC0
  Sync unit cycle: a multiple of the bus cycle time. The inputs are read periodically at this interval (in µs).
• User-defined
  Arbitrary number up to 2³² ns ≈ 4.3 secs. Decimal point values are possible.
• Shift Time
  The Shift Time can be used to displace the SYNC0 pulse of this EL1202-0100 in relation to other terminals in nanosecond steps. If the inputs of multiple EL1202 terminals are to be read at the same time, the same value must be entered here.
• Based on input reference
  If this option is activated, then an additional “input shift” is added to the SYNC0 shift configured locally for the terminal. This value is calculated and made available by the EtherCAT master (SysMan/EtherCAT device/EtherCAT tab/Advanced Settings/Distributed Clocks/Input Shift Time/, see Fig. EtherCAT Master, Advanced Settings, Distributed Clock). As a result, all the input terminals in the system (EL1xxx, EL3xxx) read their inputs as close as possible to the time of the EtherCAT frame that will fetch them, thereby supplying the most recent possible input data to the controller.
• Enable SYNC0
  Required by the EL1202-0100.
• SYNC1
  Additional SYNC pulse, derived from SYNC0 or from the DC itself. Not required by the EL1202-0100.