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6–8
Block Transfer Programming
Publication 1771 UM006B-EN-P - June 2002
Figure 6.6
Sample Ladder Logic for PLC 3 Block Transfer
S0003
1
03
WB001:0020
2
15
EQU
A = B
A : WB001:0030
B : WB001:0020
WB001:0030
3
05
Rung Descriptions
Rung 1 - Rung one is true only at power up. It uses status word 3,
bit 03 (the PLC-3's AC power loss bit) to zero the control file of both
the BTR and BTW instructions.
Rung 2 - The equal instruction is used at power up. At power up, the
BTR and BTW control files both equal zero, so the BTW instruction
is enabled.
Rung 2 and 3 - During normal program execution, the BTW and
BTR instructions are alternately executed. The done bit of either
instruction enables the next block transfer instruction. After power
up, the BTR and BTW done bits are used to alternate reads and
writes.
RUNG NUMBER RM1
XOR
A XOR B = R
A : WB001:0030
B : WB001:0030
R : WB001:0030
RUNG NUMBER RM2
BTW
BLOCK XFER WRITE
RACK
:
GROUP
:
MODULE :
DATA:
LENGTH =
CNTL:
RUNG NUMBER RM3
BTR
BLOCK XFER READ
RACK
:
GROUP
:
MODULE :
DATA:
LENGTH =
CNTL:
XOR
A XOR B = R
A : WB001:0020
B : WB001:0020
R : WB001:0020
CNTL
LE
02
002
CNTL
1
DN
1 = HIGH
05
FB002:0150
0
CNTL
FB001:0030
ER
03
CNTL
LE
002
12
1
CNTL
1 = HIGH
DN
FB002:0220
15
0
CNTL
FB001:0020
ER
13
15064
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