Chapter 13: Token Ring Cards
Token Ring Operational Detail
SmartBits System Reference 183
The TRA command has four parameters. The first two control alter the AC byte on
outgoing frames. The second two control the connection actions.
The first parameter has four bit fields.
Note: Bits 2 and 3 control loopback. This parameter is remembered on startup and
controls the default state of the card on startup.
• 0-hasnoeffect.
• 1 - connects the card to the ring.
• 2 - keeps the card off the ring.
• 3 - keeps the card off the ring and places it under the control of bit 1.
Bit 1 controls the connection - if zero (default) the card is off the ring, if 1 the card is
placed on the ring.
Bit 0 controls the operation of the card when transmitting. If it is set then the card will halt
its transmitting machine when the card receives a Beacon, Claim or Ring Purge frame.
The second parameter has four bit fields.
Note: Bit 4 is used to switch card loopback between the ring interface unit and the
external cable. If it is unset - the default - then card loopback when the card is set as a
station will go through the external cable (i.e. loopback will just switch off the phantom
drive).
If a user wants to perform a formal connect sequence from an application then they can
program the application to do the following:
• The loopback control is set to bring the card up under the control of the connection
bit.
• The card is set up to send a single burst of 1500 frames using some suitable frame
pattern such as the media test MAC frame. The card should receive these frames
without error.
• The card can then be connected to the ring with the connection control bit.
• The card can then be instructed to complete the connection sequence as needed.
Bit 3 is used to switch the card into Test Mode. This mode of operation is designed to test
passive equipment by allowing the card to source tokens on a ring without there being an
active monitor. This sourcing mechanism bypasses regular TR connection protocols by
using the token counter to detect ring activity so it can be connected to a passive piece of
equipment and set sourcing frames with minimal delay. This mode should not be used on a
live ring!
Bits 2 and 1 control Fiber Key generation (see section below for a description of this
facility). When set to 0 - default - the key is generated as needed, when set to 1 the key is
not generated, when set to 2 the key is generated only once.
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