Micromod MOD: Modcell 2050R MODBUS Communications - Manual (Page 14)

IB-23C650M
COMMUNICATION APPPLICATIONS
Attributes in the RS-485 MENU permit the supervisory control mode to be
indicated via the set-point status display on the front of the instrument. Each
of the three characters in the status display is configurable so that the user
can choose an appropriate mnemonic to represent the supervisory control
mode.
A timeout value can be defined for communications traffic to the instrument via
the Computer Timeout attribute. An activity timer in the instrument is
initialized by the host when operation starts. This action also enables the
configured set-point status display.
The timer monitors the communications bus for activity to the instrument
within the specified timeout period. If there is no communications activity to
the instrument during the specified time, a "computer failure" is declared.
During a computer failure the controller assumes local control with I/O and
mode states as defined under "Computer Failure Setup" in the RS-485
MENU.
When the controller is receiving a set-point from the host, the set-point status
display can be configured to indicate that the host is the set-point source. The
R/L key still performs its normal function. The set-point status display
indicates changes in the set-point source ( LOC, LO1, etc. ).
Computer Control
In a computer control application, the instrument functions as a computer
auto/manual station. The host performs the PID control function with the
results communicated to the controller and then to the field.
Attributes in the RS-485 MENU permit the computer control mode to be
indicated via the control and set-point status displays on the front of the
instrument. Each of the three characters in each status display is configurable
so that the user can choose appropriate mnemonics to represent the computer
control mode and set-point status.
A computer timeout value is defined and a timer monitors communications in
the same manner as for supervisory control. When the computer is active, the
function of the AUTO, R/L and Maunal keys can be configured to provide a
signal to the computer upon which it can take some programmed action.
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