Rockwell Automation 1794-XXXX FLEX I/O High-Density Analog Modules - Manual (Page 81)

Publication 1794-UM062A-EN-P - September 2012
Module Programming 73
Program Action
At power-up in RUN mode, or when the processor is switched from PROG to
RUN, the user program enables a block transfer read. Then it initiates a block
transfer write to configure the module and send data values.
Thereafter, the program continuously performs read block transfers and write
block transfers.
Two’s Complement Binary Two’s complement binary is used when performing mathematical calculations
internal to the processor. To complement a number means to change it to a
negative number. For example, the following binary number is equal to decimal
22.
0 101102 = 2210
First, the two’s complement method places an extra bit (sign bit) in the left–most
position, and lets this bit determine whether the number is positive or negative.
The number is positive if the sign bit is 0 and negative if the sign bit is 1. Using
the complement method:
0 10110 = 22
To get the negative using the two’s complement method, you must invert each bit
from right to left after the first ”1” is detected.
In the above example:
0 10110 = +22
Its two’s complement would be:
1 01010 = –22
Note that in the above representation for +22, starting from the right, the first
digit is a 0 so it is not inverted; the second digit is a 1 so it is not inverted. All
digits after this one are inverted.
If a negative number is given in two’s complement, its complement (a positive
number) is found in the same way:
1 10010 = –14 0 01110 = +14
All bits from right to left are inverted after the first ”1” is detected.
TIP You must create the data file for the block transfers before you enter
the block transfer instructions