BACK (Burst Acknowledge) is the HART slave message transmitted to a master without a corresponding master request (i.e., without an STX). BACK messages may originate from any HART slave including but not limited to HART field devices, wirelessHART field devices, gateways, wirelessHART adapters, multiplexers, I/O systems, etc. Any product that supports a HART slaveĀ function could support Burst Mode.

When in burst mode a BACK must immediately follow every ACK from the burst-mode device. The Bursting slave device will even transmit a BACK after every ACK from other slave devices in the same loop. The Burst slave device will also recover the timing of the network if any other device in the network fails to respond. BACK messages are used by HART masters to synchronize to the network. BACK messages also indicate which master will have the opportunity to communicate (STX) next.