ProSoft Technology CLX-PVX User Manual
Page 30
Page
24 QTS-
CLX-PVX
September 2009
Number, percent
High byte, hex
Low byte, hex
Number, hex
113.97%
71
F8
71F8
Modules like thermocouples linearize the inputs to percent of range, 1 to 5V.
Add-on instructions for RSLogix 5000 to convert between PROVOX percent and
ControlLogix real numbers are available from the downloads area of the Rockwell
Automation support website
In the Sample Code Library, search for
“AOI for QTS-CLX-PVX PROVOX Module REV”
Converting PROVOX Percent Format to ControlLogix Real
For positive values (high bit of upper byte clear), add the whole number part (upper byte)
to the fraction (lower byte divided by 256).
For negative values (high bit of upper byte set), subtract 256 from the whole number part
and add the fractional part.
Example 1:
To convert 1940 hex, first note that the number is positive (high bit clear).
Convert the whole number part, 19 hex, to 25 decimal. The fractional part is 40 hex = 64
decimal. Convert it to a fraction = 64/256 =.25 and add the whole number part to get
25.25%.
Example 2:
To convert E780 hex, first note that the number is negative (high bit set). Subtract 256
from the whole number part (E7 hex = decimal 231), to get -25. The fractional part is 80
hex =128 decimal. Convert it to a fraction = 128/256 = .5. Add the parts to get -25 + .5
= -24.5%
Converting ControlLogix Real to PROVOX Percent Format
For positive values:
1. Convert the whole number part and store it in the upper byte.
2. Multiply the fractional part by 256 and store it in the lower byte.
For negative values:
1. First add 256 to the whole part. If the fractional part is non-zero (in practice,
greater than .039), subtract 1 from the result. Store the result in the upper
byte.
2. Subtract the fractional part from 1 and multiply the result by 256. Store the
result in the lower byte.