Allen-Bradley 1779-KFMR User Manual page 178

Chapter 12
Below, we explain what each field specifies:
UL (Use Layer) — This one-byte field specifies whether the command
sets a parameter in the local node interface or in a remote node interface.
If you want to set a parameter at the local node, enter a UL value of 0.
If you want to set a parameter at a remote node of the local Data
Highway II link, enter a UL value of 2.
If you want to set a parameter at a remote node of a remote Data
Highway II link, enter a UL value of 3.
RT (Route) — This variable-length field specifies the destination node.
If you specify 0 for the Use Layer (UL), eliminate the route field.
If you specify 2 for the Use Layer, include a one-byte route field to
specify the destination node (001 — 376 octal) within the local Data
Highway II link. The value of this field corresponds to the octal
address selected with the LINK-ADDRESS thumbwheel switches on
the front of the remote interface.
If you specify 3 for the Use Layer, include a two-byte route field to
specify the destination link (000 — 377 octal) in the first byte and the
destination node within the destination link in the second byte.
TL (Target Layer) — This one-byte field specifies the layer (within the
destination interface) to which you want to send a command. The target
layer value column in Table 12.A tells you which TL value to use
depending on the type of command you are sending.
ENT (Entity) — This variable-length field is currently unused. Specify
a size of 00 hex and eliminate the entity field.
PWD (Password) — This field is only in command message packets.
This variable-length field should be four bytes long. Specify a size of
04 hex and a password value of 00 00 00 00 hex.
TNS (Transaction) — This two-byte field indicates which station
management message transaction is taking place. A complete transaction
consists of the command packet and the corresponding reply packet.
When the host computer initiates a transaction, it must increment the TNS
value to distinguish the packets of the current transaction from the packets
of the previous transaction. When another station receives a
station-management command packet from your host computer, it must
copy the TNS value into the TNS field of the corresponding reply packet.
This helps the command initiator of your host computer match each
command with the corresponding reply.