Rockwell Automation GMLC Reference Manual - Manual (Page 756)

Publication GMLC-5.2 - November 1999
Using Block Transfers 719
The returned values are converted from the floating-point format used in
the motion controllers to 32-bit 2s complement integers before being sent
to the PLC. This conversion is performed in the motion controller by
multiplying the floating-point values by the following and truncating any
remaining fractional part:
10
(Number of Decimal Digits)
The number of decimal digits (digits to the right of the decimal point) for
the returned values is fixed for all items in a given BTR, and is specified
by word 2 in the BTW data file used to request the data from the motion
controller. To recover the original value, the PLC must divide the received
integer value by the following:
10
(Number of Decimal Digits)
For example, if two decimal digits are specified and the value of the item
is 3.1415926, the value 314 (3.1415926 x 10
2 = 314.159 (truncated to
314)) is stored in the returned value file. In this case, since 314 is less than
65,535 (FFFF hex), 0000 is stored in the lower numbered word of the
word pair (the most significant word), and 314 (013A hex) in the higher
numbered word (the least significant word). The PLC must then divide
this value by 100 (10
2 ), with a result of 3.14—the original value accurate
to two decimal places.
With 32-bit integer numeric format, the range of values that can be
represented is -2,147,483,648 to +2,147,483,647. This limits the largest
values for items read from the motion controller based on the number of
decimal digits specified for the transfer as shown in the following table.