Publication 1747-RM001G-EN-P - November 2008
ASCII Instructions 10-9
ASCII Clear Receive and/or
Transmit Buffer (ACL)
Use this instruction to clear an ASCII buffer. ASCII instructions are removed
from the queue and then the Error bit (ER) is set. This instruction clears the
ASCII buffers immediately upon the rung transitioning to a true state. The
instruction works when the channel is in User Mode or System Mode
configured for DF1 Full-duplex or Half-duplex drivers. In System Mode, only
the ASCII transmit buffer can be cleared.
For OS Series C, FRN 7 and higher, the ACL instruction can also be used to
clear the DF1 communication buffers when the channel is configured for any
of the DF1 communication drivers. Select 0 for the channel number and Yes
for both the receive and transmit buffers. When the ACL instruction is
executed, any pending outgoing DF1 replies, incoming DF1 commands, and
outgoing DF1 commands are flushed. Any MSG instructions in progress on
that channel will error out with an error code of 0x0C. The DF1
communication buffers are cleared at end-of-scan or during REF instruction
execution.
In addition, for SLC 5/03 processors with OS302 Series C, FRN 7 or higher,
the ACL instruction can be used to clear the Local Passthru Queue when
channel 0 is configured for DF1 and the DF1 Remote/Local Passthru bit
(S:34/6) is set to Local. Select No for the receive buffer and Yes for the
transmit buffer.
ACL
Ascii Clear Buffers
Channel 0
Receive Buffer Yes
Transmit Buffer No
ACL
Output Instruction
Fixed SLC
5/01
SLC
5/02
SLC
5/03
SLC
5/04
SLC
5/05
•••
IMPORTANT
For OS Series C, FRN 7 and higher, when the ACL
instruction is executed with both the Receive Buffer
and Transmit buffer set to Yes while channel 0 is in
System Mode and configured for DF1, two actions
occur.
• The ASCII transmit buffer is cleared and any AWA
and AWT instructions in the ASCII queue are
removed.
• Any pending outgoing DF1 replies, incoming DF1
commands, and outgoing DF1 commands are
flushed.
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