Solartron Metrology AMETEK ORBIT ACS Series, Manual

Page: 49 / 63

16.2.2 Modbus Unit ID
Each Modbus message contains a Unit ID (address), the servers listen to the Modbus communications and if they hear a message
containing their UnitID they accept this message and respond. The SI100 and SI200 can have their address set in the COMMS
menu.
16.2.3 Parameters
Each Slave unit will have within its help structure or documentation a ‘Parameter Map’, which details all the Parameters that are
available, the conditions they are constrained by (limits, read / write privileges etc) and the function of the Parameter.
Modbus ‘Registers’ are 16 bit registers; often within industrial applications these 16 bit registers are ganged together to represent 32
bit data and 64 bit data, as well as floating point type information and Strings. The details about the number of registers a ‘Parameter’
consumes should be clearly detailed within the unit’s documentation.
It is, however dangerous to read the 16 bit registers that make up a more complex ‘Parameter’ individually with separate message,
as there is no way of knowing if the data was updated in-between reads, resulting in a corrupted value once the complex ‘Parameter’
is re-constructed.
The SI Series of products protect against this issue and will not allow the individual registers of a more complex parameter to be read
individually, they must all be read with a single ‘Read Multiple Registers’ type command.
An Integer type parameter (consisting of a single or multiple 16-bit registers), can also include information to several decimal places.
This is indicated within the Parameter Map by way of an inferred decimal place position; a Parameter with a decimal place position
defined as ‘0’ has no decimal places included, a decimal place position of ‘3’ for instance would mean three decimal places of
accuracy are included in the integer value.
503110 - Orbit ACS Manual Issue 9 49 of 63