Multi-timestamp terms

Some basic terms relating to the multi-timestamp function are described below. These are based on the chapter Sampling of digital inputs.

Cyclic process data/PDO

Each channel has 2 different types of cyclic PDO:

• Diagnostics/status/control values created specifically for the buffer
• The actual "values" as time-stamped Boolean data in the form of an array. The array should be set to a suitable size in the configuration. It cannot be changed during runtime.

See chapter Process image EP1258-0502.

Parameter data/CoE

Each channel has a parameter range 0x80n0:ff in the CoE directory with suitable settings, e.g. to configure the buffer or the input behavior.

Buffer

Each channel has its own buffer (memory) for 32 events, based on the FIFO principle. It is operated via the channel's own PDO, see chapter Process image EP1258-0502.

The channel state is queried for its switching state 0/1 based on the microcycle. Any changes that are detected are stored in the buffer. Depending on the configured multi-timestamp factor of the channel (MTSF), the buffer content is retrieved completely or in several steps by the controller/PLC via EtherCAT.
The behavior in the event of a buffer overflow can be configured. An overflow of the buffer is displayed in the process data. If necessary the buffer can be emptied by the controller.

Event

An event is a signal edge at a digital input, i.e. the change of the input state from 0 to 1 or from 1 to 0. The timestamp and state 0/1 are saved for each event after the change.

Timestamp

Originally, the EtherCAT distributed clocks time has the following properties: start time 1.1.2000 00:00, 64-bit scope with 1 ns resolution (~ 584 years). In order to avoid redundant process data, the multi-timestamp terminals operate with a reduced timestamp width of 32 bits (~ 4.29 sec.). Input events must be processed within 4.2 seconds, otherwise an overflow will occur and the time actually recorded will no longer be saved.

MTSF: Multi-timestamp Factor

In the configuration each channel can be configured to a fixed, maximum number of events that can be transferred per EtherCAT cycle. This means that a maximum of the same number of events can be exchanged with the controller/PLC per cycle. These process data are to be understood as placeholders, which are not all to be filled at all times.

The number of input events placed in the process data for the controller by a channel matches the number of events that arrived at the input during the last cycle or are still in the buffer.