Preface
MicroLogix 1000 Programmable Controller User Manual
13–6
Using Status Bits
Read/Write:
READ
ignore if timed out:
0
TO
Target Device:
SLC500/ML1000
to be retried:
0
NR
Control Block:
N7:0
awaiting execution:
0
EW
Local Destination File Address:
***
Target Node:
0
error:
0
ER
Target File Address:
***
message done:
0
DN
Message Length in elements
***
message transmitting:
0
ST
message enabled:
0
EN
control bit address:
N7:0/8
ERROR CODE: 0
Error Code Desc:
MSG Instruction Status Bits
The right column in the display above lists the various MSG instruction status bits.
These are explained below:
•
Time Out Bit TO (bit 08) Temporarily set this bit (1) to error out (error code
37) an existing MSG instruction. This bit has no effect unless the ST bit has
first been set due to receiving an ACK (an acknowlege). Your application must
supply its own timer whose preset value is the MSG timeout value. This bit is
reset on any false-to-true MSG rung transition.
•
Negative Response Bit NR (bit 09) is set if the target processor is responding
to your message, but can not process the message at the present time. The NR
bit is reset at the next false-to-true MSG rung transition that has a transmit
buffer available. It is used to determine when to send retries. The ER bit is also
set at this time. Use this feedback to initiate a retry of your message at a later
time. This bit is used with DH-485 protocol only.
•
Enabled and Waiting Bit EW (bit 10) is set on any false-to-true MSG rung
transition. This bit is reset when an ACK or NAK (no acknowledge) is
received, or on any true-to-false MSG rung transition.
Note
The operation of the EW bit has changed since Series C.
•
Error Bit ER (bit 12) is set when message transmission has failed. The ER
bit is reset the next time the MSG rung goes from false to true.
•
Done Bit DN (bit 13) is set when the message is transmitted successfully. The
DN bit is reset (cleared) the next time the MSG rung goes from false to true.
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