Modbus Protocol; Implementation Information - ABB AquaMaster 3 Manual

AquaMaster 3
Electromagnetic flowmeter

1 MODBUS Protocol

AquaMaster 3 RS485 MODBUS option implements the MODBUS over Serial Line protocol described in
the following MODBUS publications:

MODBUS Over Serial Line – Specification and Implementation Guide V1.02. Dec 20, 2006.

MODBUS Application Protocol Specification V1.1b. Dec 28, 2006.
Section 1.1 provides specific AquaMaster 3 MODBUS implementation details and section 1.2 provides
an overview of the AquaMaster 3 MODBUS Register mapping.

1.1 Implementation Information

The following information should be considered when implementing a MODBUS master to communicate
with AquaMaster 3:
Transmission mode:
Response time-out:
Turnaround delay:
Interface power-up considerations.
The AquaMaster 3 MODBUS interface has been designed for low power consumption so that it can
be used with battery or renewable energy supplies (as well as with mains power).
When the AquaMaster 3 MODBUS interface is inactive (no characters received for 10s) it is switched
into a low power state. In this low power state it is not possible for AquaMaster 3 to receive the first
characters sent to it although the interface will be 'woken up' within 1s by communications activity.
Therefore, after any period of inactivity longer than 10s it is necessary for a MODBUS master to
perform 1 retry to communicate with AquaMaster 3s.
MODBUS Tables Supplement COI/FET2XX/MOD/TBL-EN
Remote Terminal Unit (RTU) slave.
1s
800ms
MODBUS Protocol
2