Rockwell Automation 2711 PANELBUILDER SOFTWARE USER MANUAL User 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

Bit Numbers

БББББ

17 16 15 14

БББББ

13 12 11 10

ББББББ

7 6 5 4

БББББ

3 2 1 0

БББББ

Word X

БББББ

ББББББ

БББББ

Word X+1

БББББ

ББББББ

БББББ

Table 4.H

shows the number of bits required for different numbers of

BCD digits: