Specifications

Page 19–4
FOCUS System Manual
At the location where the Master device is
connected, configure the PLD module at this
terminal as the “Head” module. To configure the
“Head” for internal addressing, the module must
first be mapped to a DS0 channel. Mapping of the
“Head” module is accomplished by a single
mouse click on the module end and a double
mouse click in the desired T1/E1 stream and DS0.
During the mapping process, FCS will prompt,
Do you wish this module to be a “Head” or “End”
module?” Selecting “Yes” displays another dialog
box where the choice of “Head” is made. In the
same dialog box is the choice of “Internal
Address” and the assignment of the unique
address. When you select this option, FCS auto-
matically assigns the “Head” module the address
“0” (zero). The “Head” module designation means
that the module’s time slot is mapped as a drop
connection in both directions of transmission on
the DS0 time slot, just as with external addressing.
You then configure the last PLD module in the
chain as the “End” module and the remaining PLD
modules as “Remote” modules. The “Remote”
module designation means that, in the receive
direction, (in the direction toward the “Head”
module), the incoming DS0 time slot is dropped
and also passed through, while the transmit
direction is in pass-through mode only. As part of
the configuration, the user assigns each PLD
module a unique address. The address may be any
number between 001 and 255 and must be 3-
digits.
Once the network is configured, you use a
terminal emulation program (e.g., the
“HyperTerminal” application supplied with
Windows) and the device attached to the “head”
PLD module to communicate with the remote RS-
232 devices in the chain by logging onto the
“remote” or “end” PLD modules.
The operation begins when you “log in” to the
“head” PLD module, using the password assigned
to that PLD chain. (For login and connection
instructions, please refer to the testing instructions
for internal address mode in the “Acceptance
Test” section later in this chapter.) When
prompted, you enter the address of PLD module to
which the target device is attached. All the PLD
modules in the chain will receive the message, but
only the one with the matching address responds.
It does this by signaling the Maintenance Module
(in the same chassis) to supply a return path once
the return path is made available (this may take up
to 12 milliseconds). The remote PLD module then
responds to the “head” module with the message:
“PLD X transmitting,” where “X” is the module’s
address. At this point, a “somewhat” transparent
data path exists between the two RS-232 devices.
To end the connection and make a call to another
PLD module and its connected device attached,
you enter the command: “new call.” The “head”
PLD module then tells the Maintenance Module
to close the current connection path between the
two devices, that is, to “log out,” and then prompt
you for the new address. When successfully
connected, the PLD will respond “PLD XXX
transmitting” where “XXX” is the module’s
address. To end the connection without making
another call, you type the command “hangup”.
This causes the “Head” PLD module to tell the
Maintenance Module to close the path between
the two devices and “log out” from the “Head”
module.
Note that if two PLD modules on the same chain
have the same address, the “head” module will
communicate with the closest one.
19.2.3 MODEM
We recommend that you use a good quality
external modem (i.e. U.S. Robotics’ Sportster

)
for communications within a PLD network (either
internally or externally addressed). We have
found, through testing, that low quality modems
cause unpredictable communications problems
due to inconsistencies in modem operation.