• Verify that the host work station controller’s (WSC) capacity has not
been exceeded.
• Verify that the device is properly terminated. A peripheral is terminated
when its twiaxial port has two 54.9 ohm resistors located between the “A”
phase pin & earth ground and the “B” phase pin & earth ground. Termination
is provided by a “Y” or “T” cable assembly or by a terminating balun (i.e.
ASFT series).
• Verify that there are no polarity reversals in the cable.
• Verify that the cable distance does not exceed the GEMINI EXPRESS
MULTIPLEXER specification.
• Verify that the cable is data grade.
• Verify that the wiring uses natural pairs.
• Verify that the wiring avoids sources of environmental noise.
• Verify that the balun’s pinout matches the GEMINI EXPRESS
MULTIPLEXER ’s pinout.
• Verify that the host side balun’s pinout/polarity match the device side balun’s
pinout/polarity.
Devices interfere with each other!
• Verify that there is one host-polling group per GEMINI EXPRESS
MULTIPLEXER polling group.
• Verify that devices on star segments have unique addresses.
• Verify that all devices are properly terminated.
Devices cannot operate in Express mode!
• Verify that the host and the device are capable of Express mode.
• Verify that all interconnecting components support the Express mode.
• Verify that all devices on the port are Express ready.
• Verify that all cable distances are within the Express specification.
• The controller may have down shifted to 1MBPS due to errors during
installation. The controller will retry the Express mode in approximately one
hour.
Flashing Express LEDs!
• Determine the number of Express devices on the port. If there are less than
seven devices, the flashing Express LED is normal.
Express LED on without data activity!
• If the host is disconnected during an express connection, the express LED
remains on.
INTRODUCTIONINTRODUCTION
This user's manual presents the GEMINI EXPRESS MULTIPLEXER for use with
the IBM 5250 protocol. The 5250 family of products consists of the IBM's
System 34, 36, 38, and the AS/400 along with many supporting devices
manufactured by IBM and other companies. The GEMINI EXPRESS
MULTIPLEXER works with all supporting devices that are designed within the
5250 specifications.

GEMINI EXPRESS MULTIPLEXER

Decision Data’s MULTIPLEXER Gemini Eight-Port Express Fiber Optic
Multiplexer offers the unique ability to allow multiple AS/400 controller polling
groups to be transmitted over a single fiber optic pair. This feature allows all new
AS/400e controllers to provide their maximum throughput potential, in either
1Mbps Optimized or 2Mbps Express mode, by transparently multiplexing the
"split-polling" feature without requiring performance robbing PTF's. All new
IBM controllers support the "split-polling" feature as a means of achieving higher
throughput rates, even when connected to standard legacy devices. The Gemini
Express Multiplexer allows the "split-polling" feature to remain "enabled" with
performance of up to 4 times greater than standard legacy 1Mbps 5250 protocol.
The Gemini Express Multiplexer has 8 Shielded RJ45 port connections as well as
a DB25 "direct-connection" eliminating the need for the twinax "brick" and
associated twinaxial cabling. Link connectivity is via ST fiber optic multi-mode
connection with ability to operate in both point-to-point and multi-point "ring"
topologies, reducing hardware requirements by up to 50%. Other features include
Advanced Noise Filtering, LED Port Diagnostics, Configurable UTP Pin
Assignments, and a Field Replaceable wide-ranging Power Supply.