Enron Modbus I/O Addressing

Standard Values

For standard reads and writes, the address can be entered directly into the address field. Unlike with the standard Modbus driver there is no need to indicate the data type (e.g. /FLOAT) because each data type has its own predefined address range.

Register Numbers	Type	Table Name
1001-1999	Read-Write	Boolean variables
3001-3999	Read-Write	16 bit Short integer variables
5001-5999	Read-Write	32 bit Long integer variables
7001-7999*	Read-Write	32 bit Floating point variables

*Many devices allow floating point addresses above 7999.

History Logs

Note: The history logs can only be read in conjunction with an Enron History Log tag. See the Enron History Log Tag section for details on both the tag and the history storage methodology.

Analog Status tags, which store history information, should use the address structure:

HL:x:y

where x is the address of the history log (usually 701 or 702) and y is the variable's position in the returned history record (beginning with 0).

Alarm/Event Logs

An Enron Modbus device has a single log where both alarm and event information is stored. It should be noted that the alarms logged here are internal to the device and to the device's flow calculations, and as such are not necessarily related to alarms in VTScada.

Along with the timestamp, four pieces of information are returned as part of each event/alarm. Each of these pieces of information should be captured in its own analog status tag with the address:

EL:x:y

where x is the address of the alarm log (usually 32) and y is a value between 0-3 based on the chart following.

Address Index	Description	Comments
0	Bitmap	Group of flags describing the event/alarm (see following)
1	Register	Register that was changed/that triggered the alarm
2	Data1	Previous value (event) or current value (alarm)
3	Data2	Current value (event) or not used (alarm)

The Bitmap is a group of flags whose meanings change based on whether the record is an event or an alarm. Of particular importance is bit 9, which is always a 1 for an event and a 0 for an alarm.

Bit Number	Alarm Map	Operator Event Map
0	unassigned	Fixed Value
1	unassigned	Zero Scale
2	unassigned	Full Scale
3	unassigned	Operator Entry Work Value
4	unassigned	Boolean Fixed Bit
5	unassigned	Fixed/Variable Flag
6	unassigned	Table Entry Change
7	unassigned	System Command Change
8	unassigned	unassigned
9	Operator Change Event Bit (Always 0)	Operator Change Event Bit (Always 1)
10	Lo-Lo Limit	Lo-Lo Limit
11	Lo Limit	Lo Limit
12	Hi Limit	Hi Limit
13	Hi-Hi Limit	Hi-Hi Limit
14	Rate of Change Limit	Rate of Change Limit
15	Set/Reset Alarm (1 = set, 0 = reset)	unassigned

The diagram following details the tag setup. Contrasting this with the diagram of the historical log, you can see that no intermediary tag is necessary between the driver and the status tags. However, you may still choose to add a context tag to group the four analog status tags together.

Omni Flow Computers

The prefix of S8: can be used to denote that an address will return an 8 character string. For example, S8:4001 will interpret the data from address 4001 as an 8 character string.

You can read bit values from registers and history log entries by using a / or \ followed by the bit number to read.
Note that bit writes for non-boolean registers are NOT supported.