Send Blocks

On the basis of the communication protocol, it is sensible to restrict the data types at one send block to one type. Therefore, there are five types of send blocks:

• send of status values
• commands
• real values
• setpoints
• discrete values.

These types are mapped to the IEC1131 data types BOOL, REAL and DINT.

Operating Modes of the Send Blocks

The send blocks know three operating modes to send their data

• caused by request pin (SEND),
• send in connection with a change of data (AUTO), or
• cyclic send of data (CYCLE).

Send via Request Pin

The SEND signal is evaluated on the rising edge. The RDY signal remains applied for one computation cycle. If a rising edge is generated again at the SEND signal although no acknowledgement has yet been received from the receiver, the OV pin is set in order to indicate that an overrun has taken place. The evaluation of the receive acknowledgement is carried out before the evaluation of whether transmission is to take place. This means, assuming that there is an appropriately fast telecontrol link, that in connection with change-driven and cyclic transmission, a transmission job can be sent in connection with every computation of the block. In connection with send via the request pin it is possible to send only in connection with every second computation (send takes place only with a rising edge).

Change-driven Send of Data

Data are always sent when the value of the input variables changes. When changes take place, there is an internal simulation that the SEND pin changed from 0 to 1.

In order to prevent unnecessarily frequent send in the event of mild fluctuations in the input value, a threshold value can be configured for real values and setpoints. The input value is not sent until it differs positively or negatively from the value last sent by more than the threshold value.

If the input value changes again although no acknowledgement has yet been received from the receiver, the OV pin is set in exactly the same way as in connection with send via the Request pin. If an error occurs during send, the job is automatically retried until the value has been sent without error.

Cyclic Send

The data are automatically sent after the expiry of a configurable cycle time (SCANDOWN). This cycle time is indicated in multiples of the task cycle time in which the block is computed. In this operating mode, an overrun error can occur if the transmission is faster than the response time of the receiver. For setpoints, it is necessary to ensure that an acknowledgement is generated by the receiver which is not sent until the setpoint is accepted. The send block is not ready for transmission again until after this acknowledgement has been received.

Timestamps

Timestamps for data types with time associated to the data are generated when a data point is being given to the underlying protocol. So for example on the rising edge of the SEND Pin. For values where an explicit timestamp different from the actual time is required, a new group of Function Blocks has been created all ending with the extension _ET.

Note

All timestamps are only send at all if the correct IEC60870 data type with timestamps has been configured.