Page 8 • MNFL003 ║ Issue/Rev. 0.1 (9/13)
2 – Implementing Remote Host Functionality
2.1 Implementing Host Status Polling
To implement routine polling loops, the following coils should be periodically read. These
coils represent the critical states that a host should monitor.
Coil State
0 In Program Mode – Set when Program mode is accessed, via communications
or keypad
1 Checking Entries – Active when exiting Program mode, during the validation
phase
2 Program Mode Value Changed
1
– Active after exiting Program mode when
changes made
3 Power-fail Occurred
1
– Set on powerup
4 Printing in Progress – Set when printing a report (if a port is configured as a
Printer)
Coil State
264 Alarm Active
2
– Active when an alarm condition is present
266 Product Flowing – Active when the flow rate is nonzero
267 Permissive Not Met – Active when the transaction is in progress but a
permissive input is de-asserted
1 – These flags are clearable by writing a 0 to the coil using Modbus Function 5 or 15.
2 – Writing a zero to the Alarm Active coil will effectively clear all active alarms (assuming the condition no
longer exists).
2.2 Implementing Host Control (Automation) Interface via Modbus
2.21 Special Modbus Registers for Host Control
Certain registers are “trigger” registers that invoke a host automation command such as
a prompting function or a remote authorization function. These registers are listed here.
Note that some of these “trigger” registers require other registers have valid argument
values prior to invoking the command trigger.
Registers that are “trigger” registers will be designated with the superscript symbol † in
the appendix. Registers that act as arguments for a trigger register are in italics.
2.22 Host Command Result Status Register
For each write to a trigger register that implements a host command, the result of the
operation will be left in the Host Result register (Function 4, register 3590). If the com-
mand was executed successfully the value in this register will be 254. Otherwise the
value in the register will be set to one of the following error codes indicating the opera-
tion was not completed for the reason described below:
01 In Program Mode
02 Released
03 Value Rejected
04 Flow Active
05 No Transaction Ever Done
06 Operation Not Allowed
07 Wrong Control Mode
08 Transaction In Progress
microFlow.net Liquid Modbus Communications Manual Implementing Remote Host Functionality
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