ProSoft Technology MVI56E-MNET/MNETXT - Manual (Page 133)

MVI56E-MNET / MNETXT ♦ ControlLogix Platform Reference
Modbus TCP/IP Interface Module User Manual
ProSoft Technology, Inc. Page 133 of 181
April 23, 2014
Counters are available in the Status Block that permit the ladder logic program to
determine the level of activity of the server driver.
An exception to normal processing is when the pass-through mode is
implemented. In this mode, all write requests are passed directly to the processor
and are not placed in the database. This permits direct, remote control of the
processor without changes in the intermediate database. This mode is especially
useful for Client devices that do not send both states of control. For example, a
SCADA system may only send a SET command to a digital control point and
never send a CLEAR command to that same digital point address because it
expects the processor logic to reset the control bit. Pass-through must be used to
simulate this mode. The following illustration shows the data flow for a server port
with pass-through enabled.