Rockwell Automation 1746-XXXX SLC 500 4-Channel Analog I/O Modules User Manual - Manual (Page 97)

1 Publication 1746-UM005B-EN-P - June 2004
Appendix
B
Two’s Complement Binary Numbers
The SLC 500 processor memory stores 16-bit binary numbers. Two’s
complement binary is used when performing mathematical
calculations internal to the processor. Analog input values from the
analog modules are returned to the processor in 16-bit two’s
complement binary format. For positive numbers, the binary notation
and two’s complement binary notation are identical.
As indicated in the figure on the next page, each position in the
number has a decimal value, beginning at the right with 2
0
and
ending at the left with 2
15
. Each position can be 0 or 1 in the
processor memory. A 0 indicates a value of 0; a 1 indicates the
decimal value of the position. The equivalent decimal value of the
binary number is the sum of the position values.
Positive Decimal Values
The far left position is always 0 for positive values. As indicated in the
figure on the next page, this limits the maximum positive decimal
value to 32767 (all positions are 1 except the far left position). For
example:
0000 1001 0000 1110 = 2
11
+2
8
+2
3
+2
2
+2
1
= 2048+256+8+4+2 = 2318
0010 0011 0010 1000 = 2
13
+2
9
+2
8
+2
5
+2
3
= 8192+512+256+32+8 = 9000