On-line Configuration

Configuring the unit via the Modbus master and the network might seem to be the

simplest method at first sight, but there are a number of practical difficulties with this

configuration technique.  This approach means that the user must deal with a number

of complex aspects which require a significant investment of the configurer’s time

before they are understood fully.  A further difficulty may be a lack of the necessary

memory space within the Modbus master.  If the configuration is likely to be changed

frequently it could even be necessary for the system designer to design specific ‘user

interface’ screens, such as those used by the PC software, to allow changes to be

made by operators.  This would be a time consuming and costly task.

For most users, the attraction of being able to use the Modbus master to configure the

unit is that the configuration can be re-sent if the slave’s memory becomes corrupted.

Whilst this is true, it is not possible to avoid the difficulties (and costs) outlined earlier

and the decision to adopt a strategy of configuring via the Modbus master should be

arrived at only after due consideration.

A cost effective compromise would be to perform the initial configuration via the PC

software, and then read the configuration parameters stored in the MTL838C via the

host.  The stored parameters could then be re-written to the MTL838C should the

configuration database ever become corrupt.

If a user intends to adopt the on-line configuration method, the calculation of

configuration parameters for storage in the master can be simplified, and the

possibility of ‘human error’ reduced, by using the PC software to input the required

data and data format, and then reading the stored values (encoded correctly in the

required data format) back from the MTL838C via Modbus.  The user should still realize

that any subsequent alterations of the parameters will require further use of the PC

software.