137001UA
1-2
Operation
P
ATTON
E
LECTRONICS
C
O
.
I
NSTALLATION
A
ND
O
PERATIONS
M
ANUAL
3012-14-18/V24
Channel Selection Modes (4 and 8 port only)
The Patton MSD provides two selectable sub-channel service modes of operation:
Scanning Mode and Priority Mode. Depending on system requirements, either mode
may be selected by internal DIP switch settings. Both modes switch on activity from
the sub-channel. Activity is defined as raising RTS on a sub-channel.
In the Scanning Mode the Patton MSD scans each sub-channel in sequence,
beginning with channel 1. This rotational sequence is repeated continually with each
attached sub-channel having equal access to the communications link. When RTS
from a sub-channel becomes active, that sub-channel is given a CTS signal and
switched through to the master port by the MSD. All remaining sub-channels are
locked out until the first device becomes inactive. When the sub-channel device
becomes inactive, the MSD will resume scanning the sub-channels for another active
signal.
When configured for Priority Mode operation, the Patton MSD monitors all sub-
channels simultaneously with sub-channel 1 having the highest priority. When a sub-
channel becomes inactive, the MSD will automatically default to the highest priority
(lowest number) sub-channel with activity.
Port Enable/Disable front panel switches must be pushed in (
GREEN
indication) for
a sub-channel to access the main channel, regardless of the mode of operation
selected.
Anti-Streaming
A typical problem often encountered in DDS and leased-line, polled environments is a
“Streaming” remote terminal. The streaming problem can tie up an entire circuit until
the offending terminal has recovered or is powered down. A streaming condition
occurs when a sub-channel remains active, disrupting the polling sequence. The MSD
provides two user selectable modes of controlling a streaming condition: an
automatic Anti-Streaming Abort Timer, and a manual Operator Control mode (front
panel push button switch).
The streaming condition caused by one of the attached terminals can be quickly
bypassed by the Patton MSD via the associated front panel locking switches. A
switch is provided for each sub-channel and permits the rapid removal of a
streaming terminal without having to disconnect any cables or power down the
offending terminal. Terminals may be selectively removed for self-test and
maintenance without affecting the remaining sub-channels. Once the streaming
condition has been corrected, the front panel switch is simply depressed to the
locked (Enable) position (Green indicator
ON
) to re-establish normal operation.
