The E2050 is interconnected to other E2050 modules in systems that require
the sharing of the output channel or where each system handles one type of
channel and TNPP packets are received for both. The diagram below shows two
systems interconnected by dedicated ports E and F. The significance of this
is that there are two types of communication on the same port.
STOP/CONTINUE:
The first type is a STOP/CONTINUE
command set which each system uses to tell the other system to perform that
command as soon as possible. In the current configuration this command set
is used for priority messages. The command is not acknowledged, it is simply
broadcasted to the other system.
The STOP command is
received immediately and sets a STOPBATCH flag. The system will shutdown as
soon as possible, usually it stops buffering messages immediately and
continues to empty the currently populated buffers. The system will shutdown
once the buffers are empty.
If one system has received a
priority and the other system has the network, it sends a STOP command to
the other system. It immediately buffers the priority and waits for the
other system to dekey. Once the other system dekeys the current system keys
up and delivers the message.
If the current system
receives a priority and it is using the network it also sends a STOP
command. This hinders the other system allowing the current system to
shutdown if the message is for the wrong baud rate. The current system
dekeys then rekeys on the correct baud rate.
If the
current system receives a priority and it is on the correct baud rate, it
simply splices it into the exiting data stream.
A CONTINUE
command is sent at the end of any batch where there are no priority messages
in buffers or in queue. The systems then continue as normal.
If both systems contain a priority then both are issued with STOPS. However
the priority messages will not be sent and received at exactly the same time
due to the state machine operation of the systems. Therefore on receipt of a
priority message any system on a STOPBATCH command is immediately cancelled
and the system will operate normally. It will then deliver the priority,
then send a CONTINUE to the other system allowing the other system to
process its own priority.
CHANNEL Control:
The second type of command is simply a STX packet not meant for the current
system. In this case the TNPP packet is examined for the Channel
field and if it is not for the current system it automatically sends it to
the other system. It does not know what the other system is and assumes it
is for another system. If the TNPP packet is not meant for either system it
gets dumped by the second system. This prevents the packet circulating
between two systems if the Channel field is not for either system.
In this technique Port E is a normal port but port F is the dedicated to the
purpose of sending information to the other system. Port E can receive these
special packets as well as normal messaging packets. This technique also
allows the system to determine where the packet came from by the port and
how to handle it.
Ports B and D operate
as normal. Both accept packets intended for either system. The decision to
send data to the other system is based on the STX packet Channel field
contents.
These commands require a response.
STX packets require an ACK,NAK or CAN response. ENQ and SYN packets also
require ACK responses. The current system runs the packets in a simplex
mode, that is a packet is sent and it waits for a response before moving on
to the next packet.
When there are two systems and the packet is to be sent
from the receiving system to the other system, then the first system
operates in a transparent mode. e.g.
A STX comes in Port B system 1. It is redirected out Port F System 1. This is sent transparently
to the normal processing of packets. It is
received in Port E system 2 The packet is accepted and a response is sent.The ACK leaves Port E system 2 It is
received in Port F System 1. System 1 remembers the packet was from port B. It sends the same ACK out Port B system 1. Original Sender
gets the response from the terminal server.
CHANNEL Selection:
All E2050
have the same firmware. A dip switch is provided on the the E2050 to help
select the Channel requirements. The dip switch selects the Channel and the
processors selects that Channel in the firmware at startup and sets the
Channel optos which do two tasks. It provides a visual indication via the
optos and the E2051 backplane as to that selection. The E2019 uses these
control lines to provide a visual LED indication that the channel has been
selected and it allows the E2019 to decide what PURC sequence to transmit
relevant to the channel.
