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APPENDIX B – MODBUS Communications
MODBUS Register Formats
These extended MODBUS holding registers come in a variety of formats. These formats
are described here.
Int
The Int type is a signed 16-bit integer number. It is the basic MODBUS register.
Long
The Long is two MODBUS registers sent consecutively to form a 32-bit value. The first
register contains the sign bit and the 15 most significant bits of the value. The second
register contains the remaining 16 least significant bits.
Time
The Time format is three MODBUS registers sent consecutively to form a date-time
group encoded thus:
Upper 8 bits
Lower 8 bits
First register
Month (1 - 12)
Day (1 - 31)
Second register
Year (0 - 199)
Hour (0 - 23)
Third register
Minute (0 - 59)
Second (0 - 59)
Mod10 x 3
The Mod10 x 3 format is three MODBUS registers sent consecutively to form a 12-digit
decimal value encoded thus:
First register:
4 least significant (of 12) digits of complete value, in binary
(0 - 9999)
Second register:
4 middle (of 12) digits of complete value, in binary (0 - 9999)
Third register:
4 most significant (of 12) digits of complete value, in binary
(0 - 9999)
Therefore, the complete value is (R3 * 10^8) + (R2 & 10^4) + R1. This format can
accommodate values from 0 to 999,999,999,999 decimal.
Display
The Display format varies depending on the exact definition of a given display item by
the user. Meter Displays can contain a numeric value expressed as a Long or a Mod x 3
format with a primary scaling factor, a Long format without scaling, or a Time format.
Each Display has a corresponding Register Description (see Reg Desc below) that
contains, among other things, a "Format Type" field that explains how to interpret that
Display's data.
LP Record
The Load Profile Record contains the Load Profile data for a single interval. This format
consists of a time stamp (in the Time format described here) followed by 1 to 12 pulse
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