Ethernet Communications Modules, 3rd Edition, Rev. D
4–18
Chapter 4: RLL Programming for Communications
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A
B
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D
Our three RX/WX instructions can be
sequenced by the two contacts C50 and C51.
Two contacts provide four different binary
states:
• Both off
• C50 on and C51 off
• C50 off and C51 on
• Both on
We only need to use three of the four binary
states (circled) since we only have three RX/WX
instructions to sequence.
First RX/WX Instruction
Truth Table C52 C51 C50
First RX/WX 0 0 0
Second RX/WX 0 0 1
Third RX/WX 0 1 0
Fourth RX/WX 0 1 1
Fifth RX/WX 1 0 0
Sixth RX/WX 1 0 1
Seventh RX/WX 1 1 0
Eighth RX/WX
1 1 1
LD
K114
LD
K2
LDA
O40600
WX
VC100
SP122
C51
C51
C50
SET
C50
C50 and C51 are interlocking
contacts. They are normally closed in
this rung to permit power flow to the
first WX instruction. Both bits are
off, corresponding to the first row of
the truth table.
After the WX instruction is executed
C50 is SET (turned on) which opens
the contact in this rung and closes the
C50 contact in the next rung.
C51 is RESET (turned off) which
leaves the C51 contact closed for the
next rung.
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