Automation Direct D0-DCM, Manual, Page: 53 / 70

User Application
Guidelines
RLL
Programming
for Communications
4–15
RLL Programming for Communications
DL05/06 Data Communications Module, 1st Edition, 08/05
LD
K209
LD
K2
LDA
O40601
WX
VC0
SP122
SET
C51
C51
C50
RST
C50
C50 is normally open and C51 is
normally closed. For this rung to be
executed, the C50 bit must be on and
the C51 bit must be off, corresponding
to the second row of the truth table.
C50 was turned on in the previous
rung. C51 was turned off in the
previous rung.
After the WX instruction is executed
C50 is RESET (turned off) which
opens the C50 contact in this rung and
closes it in the next rung.
C51 is SET (turned on), which closes
the normally open C51 contact in the
next rung.
LD
K214
LD
K2
LDA
O40602
RX
VC20
SP122
RST
C51
C51
C50
RST
C50
In this last rung, C50 is normally
closed and C51 is normally open. For
this rung to be executed, the C50 bit
must be off and the C51 bit must be on,
corresponding to the third row of the
truth table. C51 was turned on in the
previous rung.
After the RX instruction is executed,
C50 is RESET which opens the C50
contact in this rung and allows it to
close in preparation for repeating the
first communication rung on the next
CPU scan (page 4-14).
C51 is also RESET, which allows the
C51 contact to close in preparation for
repeating the first communication rung
on the next CPU scan (page 4-14).
At the end of the third RX/WX instruction, we cycle back to the top row of the truth
table on page 4–14. Both C50 and C51 are off, and the next CPU scan executes the
first RX/WX instruction.
Second RX/WX
Instruction
Third RX/WX
Instruction
Returning to the
First RX/WX
Instruction