Publication 1747-RM001G-EN-P - November 2008
SLC Passthru Communications 14-5
The Local Passthru Queue Full bit is a monitor only bit that is set to a one
anytime this 30-slot local passthru queue becomes full. The local passthru
queue can be flushed at anytime by executing the ACL instruction with the
Receive Buffer set to No and the Transmit Buffer set to Yes.
When the DF1 Remote/Local Passthru bit is set to Local, any DF1 commands
received at channel 0 and passed through to channel 1 DH-485 are stored in a
30-slot local passthru queue until a reply is received from the channel 1
DH-485 network. This is done so that the the processor can determine
whether local replies received on the channel 1 DH-485 are for MSG
instructions initiated by the processor or for passthru back to the channel 0
DF1 network. If a DH-485 device that is actively passing the token does not
reply to the DF1 command, one slot in the 30-slot local passthru queue will be
lost until the next power cycle.
Using RSLinx Classic, version 2.50 and higher, with SLC 5/03
Passthru
RSLinx Classic, version 2.42 and below, only supports channel 0 to channel 1
passthru, when channel 0 is configured for DF1 Full-duplex or DF1
Half-duplex Master. RSLinx Classic, version 2.43 supports all modes of
channel-to-channel passthru described below, except when channel 0 control
line handshaking is enabled. RSLinx Classic, version 2.50 and higher supports
all modes of channel-to-channel passthru as described below.
TIP
The SLC 500 Fixed, SLC 5/01, SLC 502, ControlLogix,
FlexLogix, and CompactLogix controllers can only
respond to local DH-485 packets. Set S34/6=1 when
using SLC 5/03 channel-to-channel passthru to
communicate with the SLC 500 Fixed, SLC 5/01, SLC
502, ControlLogix, FlexLogix, and CompactLogix
controllers via DH-485 on channel 1.
TIP
As the Local Passthru Queue approaches capacity,
S34:/7 may toggle between 0 and 1. To verify that
the Local Passthru Queue is completely full, use the
Local Passthru Queue Full bit as a pre-condition to a
timer (TON) with a preset of ten seconds or longer.
Then use the timer done bit as a pre-condition for
executing the ACL instruction.
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