ESPA 4.4.4: Introduction & requirements 🔒

The ESPA 4.4.4 protocol was created in 1984 by the European Selective Paging manufacturers Association. It is a serial protocol, designed for the communication between different systems i.a the interaction among SCADA systems, paging systems, telephony systems, computers, etc...

Mostly used for the transmission of fire alarms, intruder alarms, nurse calls to alarm management systems like ALERT or to DECT telephony systems.

The ESPA 4.4.4. protocol is message oriented and uses short messages which are sent on a serial data connection, like RS-232.

In the ESPA topology there is a master unit and one (or more) slave units.

​A slave unit cannot send data over the serial link until it has been permitted to do so by the master unit. The master unit regularly polls the slave, asking it whether it has any data to send. If the slave has data to send, it will become a temporary master unit, seizing control of the data link and sending its data. Once it's done, it will return control to the master unit.

Since the protocol is created to be able to handle multiple slaves, each device has an address.

The master unit always uses the address 1, while the first slave normally uses address 2.

Sending Data with ALERT

Receiving Data with ALERT