SCRAMNET NETWORK
Copyright 2007
2-11
VME6U HARDWARE REFERENCE
In some system designs, and on some computer buses, it is not desirable or effective to
have the WRITE cycle lengthened to match network throughput—even at the expense of
possible data loss across the network. In this case this option may be disabled by setting
CSR8[1] ON. Transmit FIFO 7/8 Full CSR1[2] can then be used to control the data flow
via software control.
2.10.4 Loopback Modes
Loopback mode is used for testing, and for routing data, which would normally be
transmitted onto the network back into the node. This mode is used to check performance
internally (Wire Loopback) at the Media Card (Mechanical Switch Loopback) and
Transmit/ Receive (Fiber-optic Loopback).
WIRE LOOPBACK MODE
The Wire Loopback mode needs no manual external modifications to work. Wire
Loopback is enabled by setting CSR2[7] ON. This mode checks the on-board circuitry
for continuity.
NOTE
: If a node is inserted into the network while in wire loopback mode, it will create
a break in the network ring, making all nodes down-line unreachable.
MECHANICAL SWITCH (MEDIA CARD) LOOPBACK MODE
Mechanical Switch (Media Card) Loopback mode is enabled by setting Mechanical
Switch Override CSR8[11] to OFF. This test is used to check the circuitry up to and
including a major portion of the Media Card but excludes the fiber-optic circuitry. In this
test the signal does not leave the Media Card.
FIBER-OPTIC LOOPBACK MODE
The Fiber-optic Loopback
mode must have the optional Fiber Optic Bypass Switch
connected, Disable Fiber-optics Loopback CSR2[6] set to OFF (power up default), and
Insert Node CSR0[15] enabled to be valid. When the Fiber-optic Loopback
mode is in
effect, the output of the transmitter is connected by fiber optics directly to the input of the
receiver, and the receiver is disconnected from the network.
The optional Fiber Optic Bypass Switch must be installed for this loopback to work.
However, in the absence of the Fiber Optic Bypass Switch, fiber-optic cables could be
run from the node’s transmitter output connectors to the receiver input connectors. This
configuration, with Insert Node enabled, would constitute a Fiber-optic Loopback mode
for stand-alone testing. Set CSR2[6] ON to disable the Fiber-optic Loopback mode when
the node is in use as a part of the network. This configuration is not a substitute for the
Fiber Optic Bypass Switch for network operation.
Содержание SCRAMNet+ SC150 VME6U
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