can I access PLCs that use the ModBus protocol using Polyhedra?
The Polyhedra database has an inbuilt mechanism, the DVI, which operates in conjunction with device-specific drivers to allow the user to set up records which will be fed with values obtained from I/O devices such as programmable logic controllers (PLCs) and remote telemetry units (RTUs). The drivers are relatively simple to write, in that they are primarily concerned with handling the low-level protocol for communicating with the remote devices; it is the responsibility of the generic part of the DVI to get information into and out of the database, and to organise poll cycles where needed according to general parameters specified by the user by poulating certain interface tables in the database. Among the supported drivers is the modicon driver, that handles networks of PLCs that use the ModBus driver over serial lines (including multi-drop serial lines if supported by the hardware) at user-selectable speed, parity, etc. It allows the user to set up records corresponding to individual
