Rockwell Automation 1761 MicroLogix 1000 Programmable Controllers - Manual (Page 260)

Preface MicroLogix 1000 Programmable Controller User Manual
13–12
Application Examples that Use the MSG Instruction
Example 1
Application example 1 shows how you can implement continuous operation of a
message instruction.
Bit S:0/11 ensures that the MSG instruction will only be processed when
the active protocol is DH-485. Bit S:1/7 ensures that DH-485 is
communicating before sending the MSG. Bit B3/1 enables the MSG
instruction. When the MSG instruction done bit (N7:0/13) is set, it unlatches
the MSG enable bit (N7:0/15) so that the MSG instruction will be
re-enabled in the next scan. This provides continuous operation.
The MSG error bit will also unlatch the enable bit. This provides continuous
operation even if an error occurs.
] [
S:0
11
(U)
N7:0
15*
(EN)
(DN)
(ER)
MSG
READ/WRITE MESSAGE
Read/write
WRITE
Target Device SLC500/ML1000
Control Block N7:0
Control Block Length 7
END
] [
N7:0
13*
] [
N7:0
12*
0
1
2
* MSG instruction
status bits:
12 = ER
13 = DN
15 = EN
Operation Notes
] [
B3
1
] [
S:1
7