A–20 PQM POWER QUALITY METER – INSTRUCTION MANUAL
READING LONG INTEGERS FROM MEMORY MAP APPENDIX A: APPLICATION NOTES
A.7 Reading Long Integers from Memory Map
APPLICATION NOTE PQMAN08: READING LONG INTEGER VALUES FROM THE
MEMORY MAP
The PQM memory map contains some data which is formatted as a long integer type, or
32 bits. Because the Modbus Protocol maximum register size is 16 bits, the PQM stores
long integers in 2 consecutive register locations, 2 high order bytes, and 2 low order bytes.
The data can be retrieved by the following logic:
EXAMPLE:
1. Reading a positive 3 Phase Real Power actual value from the PQM:
2. Following the method described above:
DATA VALUE = (004F × 2
16
) + 35D1hexadecimal
= 5177344 + 13777converted to decimal
= 5191121decimal
REGISTER ACTUAL VALUE
(hex)
DESCRIPTION UNITS & SCALE FORMAT
02F0
02F1
004F
35D1
3 Phase Real Power (high)
3 Phase Real Power (low)
0.01 x kW F4
READ THE HIGH ORDER REGISTER AND
STORE THIS VALUE INTO “A”
READ THE LOW ORDER REGISTER AND
STORE THIS VALUE INTO “B”
IS THE MOST SIGNIFICANT BIT OF THE HIGH
ORDER REGISTER SET?
i.e. is HIGH ORDER REGISTER > 32767?
YES
DATA VALUE = (A x 2 ) + B
16
NO
(DATA VALUE = DATA VALUE – 2
32
)
OR
APPLY 2’s COMPLEMENT TO DATA VALUE;
THE SIGN IS IMPLIED TO BE NEGATIVE
DATA VALUE = DATA VALUE
Courtesy of NationalSwitchgear.com
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