Automationdirect.com HX-ECOM Series - Shift Register; Store if Equal

Ethernet Communications Modules, 3rd Edition, Rev. D
4–20
Chapter 4: RLL Programming for Communications
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D
Shift Register
The Shift Register can be used for creating interlocks, as an alternative to using control relays.
For a complete explanation of the function of the Shift Register, see the User Manual for
your PLC. If you have more than a few RX/WX instructions, using control relays can become
cumbersome. The Shift Register allows a single contact to be used in each communication rung
as an interlock.
Store If Equal
The Store If Equal instruction detects when
the Shift Register is reset to zeros. When
that condition is true the C60 bit is SET by
this rung. The C60 bit becomes the high bit
shifted by the Shift Register until each RX/WX
instruction is executed in turn.
The data input to the Shift Register (SR) is
Special Relay SP1. SP1 is the always-on bit.
Combined with a normally closed contact it
sends zeros to the Shift Register data input.
The clock input to the Shift Register is SP122,
the communication busy bit. Each time one
of the RX/WX instructions executes, the Shift
Register moves the set bit over one place.
C63 is used in this example to reset the Shift
Register to all zeros.
SR
SP1
C60
C77
SP122
C63
ShiftRegister after firstRX/WX.
C74C73 C72C71 C70C67 C66C65 C64C63 C62C61 C60C75C76C77
ShiftRegisterafter first scan.
C74C73 C72C71 C70C67 C66C65 C64C63 C62C61 C60C75C76C77
C74C73 C72C71 C70C67 C66C65 C64C63 C62C61 C60C75C76C77
C74C73 C72C71 C70C67 C66C65 C64C63 C62C61 C60C75C76C77
C74C73 C72C71 C70C67 C66C65 C64C63 C62C61 C60C75C76C77
ShiftRegisterafter second RX/WX.
ShiftRegister aftersecond scan.
C74C73 C72C71 C70C67 C66C65 C64C63 C62C61 C60C75C76C77
ShiftRegister after thirdRX/WX.
ShiftRegister afterthird RX/WXplus one scan.
V40603
SET
=
K0
C60