Rockwell Automation 1771-QB Linear Pos. - Manual (Page 218)

Appendix
H
HĆ1
Data Formats
Bit 3 in the parameter control word (word 1 in the parameter block) determines
the format of the data contained in block transfer reads and writes. BCD format
provides compatibility with older programmable controllers. Binary format
provides compatibility with the PLC-5, which uses integer (16-bit 2’s
complement) data. This appendix explains both these numbering formats.
BCD (Binary Coded Decimal) is a numbering format by which decimal digits
are directly represented by 4-bit groups of binary numbers. Here’s how the
decimal digits 0 to 9 are represented:
Table H.A
Binary Representation
Decimal Digit Binary Representation
0 0000
1 0001
2 0010
3 0011
4 0100
5 0101
6 0110
7 0111
8 1000
9 1001
Example: To represent the number 8761 (decimal) using BCD notation, set the
16 bits of the word like this:
1000 0111 0110 0001
8 7 6 1
Important: In BCD format, none of the four-bit groupings may contain a value
greater than 1001 (binary).
To complement a number means to change it to a negative number. 2’s
complement binary is a method used to represent signed integers in binary
notation. This method is used with PLC-3 and PLC-5 processors.
BCD
2's Complement Binary