Allen-Bradley SLC 500

QUICKDESIGNER Allen-Bradley •
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LSD - Long Word Signed Decimal
The LSD variable is similar to the WSD format. The LSD format requires two words from the data
table, which consist of six BCD digits. The two words in the data table must be consecutive, and the
high order BCD digits, as well as the sign, overflow, and underflow bits are contained in the first
(lower numbered address) word used in the data table. The format is shown below.
17 16 15 14 13 12 11 10 7 6 5 4 3 2 1 0
Not used
Underflow Bit (1 = value is between -1 and +1)
Sign Bit (1 = negative, 0 = positive)
Overflow Bit (1 = value < -999999 or > 999999)
17 16 15 14 13 12 11 10 7 6 5 4 3 2 1 0
1's Di
g
it10's Di
g
it100's Di
g
itNot usedt
Data table word at address = n
Data table word at address = n+1
1000's Digit10000's Digit100000's Digit
When the number is read, its sign will be returned from the sign bit while the overflow and underflow
bits are ignored.
Example:
The following binary value is present in a PLC2/15 at address 250 and 251.
17 16 15 14 13 12 11 10 7 6 5 4 3 2 1 0
1010000000111111
17 16 15 14 13 12 11 10 7 6 5 4 3 2 1
0
Word 250
Word 251
000 00 011 11 100100
Reading this variable would result in the value -555321 because the sign bit was set and the octal
number in register 250 is 555 and the octal number in register 251 is 321.
MSG - ASCII Text Message
The MSG variable is used to receive text messages and display them in a text field. The message is
assembled as two bytes from one PLC data word. The format of a MSG word is shown below.
17 16 15 14 13 12 11 10 7 6 5 4 3 2 1 0
Second ASCII B
y
teFirst ASCII B
y
te