Rockwell Automation 2711 PANELBUILDER SOFTWARE USER MANUAL - Manual (Page 93)

Planning Your Application
Chapter 4
4-18
Each group of 4 bits represents the equivalent of 1 digit in a numeric
value display.
Example: BCD Values or States
If you configured a BCD data value to have a maximum of 16 states (2
digits), then the assigned address would be an 8-bit contiguous string
with 4 bits for each digit.
2 digits @ 4 bits each = 8 bits
If a numeric value display was configured to have a range from 00000
to 99999 (5 digits), then the assigned address would be a 20-bit
contiguous string with 4 bits for each of the 5 digits.
5 digits @ 4 bits each = 20 bits
Since a PLC word can only support 16 bits, an additional word is
required for the additional 4 bits.
When more than one PLC word is required to support the required
number of digits, all remaining digits will extend into the next higher
word. Taking another example, BCD value 123456 would be
represented in two PLC words as follows.
Table 4.G
BCD Format
БББББ
БББББ
Bit Numbers
БББББ
БББББ
17 16 15 14
БББББ
БББББ
13 12 11 10
ББББББ
ББББББ
7 6 5 4
БББББ
БББББ
3 2 1 0
БББББ
БББББ
Word X
БББББ
БББББ
3
БББББ
БББББ
4
ББББББ
ББББББ
5
БББББ
БББББ
6
БББББ
БББББ
Word X+1
БББББ
БББББ
БББББ
БББББ
ББББББ
ББББББ
1
БББББ
БББББ
2
Table 4.H shows the number of bits required for different numbers of
BCD digits: