ERP1 Telegram Size and Duration

The telegram size of an ERP1 telegram (in bits) can be calculated for all telegram types except switch telegrams as follows:

This formula accounts for the fact that the last byte of the telegram does not use the two sync bits.

Based on the telegram size and the data rate of 125 kbit/s, the telegram transmission duration can be calculated as:

ERP1 Switch Telegram

Switch telegrams carry 1 byte of DATA payload and use 4 bit CHOICE and 4 bit HASH fields. The combined length of all telegram fields (CHOICE+ DATA + SENDER EURID + HASH) is 6 byte.

The telegram size of an ERP1 switch telegram therefore is:

The telegram duration of an RPS or a 1BS telegram is therefore:

1BS (Contact Sensor) Telegram

1BS telegrams carry 1 byte of DATA payload and therefore the combined length of all telegram fields (RORG + DATA + SENDER EURID + STATUS + HASH) is 8 byte.

The telegram size of an RPS or a 1BS telegram therefore is:

The telegram duration of an RPS or a 1BS telegram is therefore:

4BS (4 Byte Sensor) Telegram

4BS telegrams carry 4 byte of DATA payload and therefore the combined length of all telegram fields (RORG + DATA + SENDER EURID + STATUS + HASH) is 11 byte.

The telegram size of an RPS or a 1BS telegram therefore is:

The telegram duration of a 4BS telegram is therefore:

VLD (Variable Length Data) Telegram: STM 550 with D2-14-41

VLD telegrams carry a variable length of DATA payload which depends on the used EEP. For the case of EEP D2-14-41 used as default EEP by STM 550, the DATA payload size is 9 byte and therefore the combined length of all telegram fields (RORG + DATA + SENDER EURID + STATUS + HASH) is 16 byte.

The telegram size of a VLD telegram with EEP D2-14-41 therefore is:

The telegram duration of a VLD telegram with EEP D2-14-41 is therefore: