Rockwell Automation 1785-Lxxx Enhanced and Ethernet PLC-5 Programmable Controllers - Manual (Page 305)

Publication 1785-UM012D-EN-P - July 2005
Instruction Set Quick Reference D-5
Compare Instructions
Count Down
CTD
Status Bits:
CU-Count Up
CD-Count Down
DN-Count Down done
OV-Overflow
UN-Underflow
Instruction Description
CTD
COUNT DOWN
Counter
Preset
C5:1
10
35
Accum
If the input conditions go true, counter C5:1 starts
counting, decrementing by 1 every time the rung goes from
false-to-true. When the accumulated value is less than the
preset value (10), the counter resets the counter done bit.
Rung
Condition
CD
14
DN
13
UN
11
ACC
Value
CTD
Status
False
Toggle True
True
0
1
1
0
1
0
0
0
0
0
dec by 1
< preset
Disabled
Counting
Done
True 1 0 1 < -32768 Underflow
False 0 1 0 >= preset Preload
See page F-8 for a description of prescan operation for
this instruction.
Instruction Description
Limit Test
LIM
Mask Compare Equal
MEQ
LIM
LIMIT TEST (CIRC)
Low limit
Test
High limit
N7:10
N7:15
N7:20
3
4
22
If the Test value (N7:15) is >= the Low Limit (N7:10) and <= the
High Limit (N7:20), this instruction is true.
Low Limit LIM
0
-5
5
10
Test
10
0
5
11
0
5
T
T
F
T
F
High Limit
10
10
10
0
-5
10 11 T 5
MEQ
MASKED EQUAL
Source
Mask
Compare
D9:5
D9:6
D9:10
0
0000
0000
0000
The controller takes the value in the Source (D9:5) and passes
that value through the Mask (D9:6). Then the controller compare
the result to the Compare value (D9:10). If the result and this
comparison values are equal, the instruction is true.
Source MEQ
0008
0008
0087
0087
Mask
0008
0001
000F
00F0
T
F
T
F
Compare
0009
0001
0007
0007