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Appendices
Installation & Reference Guide — Doc. 5798
Encoding and Decoding the Serial Data Stream
Analog, serial, and digital signals to be sent from the control to the server are fed
into the input (left) side of an Intersystem Communications symbol which
encodes
the signals into a serial data stream, available as an output labeled
tx$
(for
transmitter
). This data stream is connected to the input side of the serial driver
symbol, also labeled
tx$
, and is sent out the COM port to the server.
Convenience feature: You can
connect an analog signal to a
serial signal input of a signal
block’s symbol. Upon receipt, the
server automatically converts the
analog value to a decimal (base
10) numeric string.
The server receives the data on a certain connection, via a certain channel number
(if TCP/IP). It searches through its active signal blocks for one with a signal range
that can accommodate the incoming signal. It also knows the signal type (analog,
serial, or digital) and sends the signal to the appropriate method implemented by the
signal block. A useful exception to this general paradigm is that when the server
receives an analog signal when it expected a serial signal (
i.e.,
the signal number
matched that of a serial signal, the server as a courtesy, automatically converts the
analog value to a decimal (base 10) numeric string.
Data from the server received at the COM port is available on the output (right) side
of the serial driver symbol, labeled
rx$
(for
receiver)
. This data must then be
decoded
by the control system into system signals it can use. To do this, the
rx$
stream is connected to the input side of an Intersystem Communications symbol, also
labeled
rx$
. The outputs of this symbol are analog, serial, and digital signals.
The
Intersystem Communications
Symbol Signal Space
The term “signal space” refers to the number of signals available to the
Intersystem
Communications
symbol connected to a given i/o stream. Specifically, there are a
total of 4096 signals available. However, while the first 1024 signals may be of any
type (Analog, serial, or digital), the remaining 3072 signals can only be used for
digital signals. An additional constraint imposed by the SIMPL Windows compiler is
that each symbol (and therefore each signal block on the server side) must list all its
digital signals after all its analog/serial signals (which may be intermixed).
Since each signal block’s signals are numbered consecutively within this space, and
since the non-digital signals of all signal blocks must be positioned below 1024, only
that portion of the space is normally of practical use.
N
OTE
:
The various signal block definition windows all provide a dynamic display of the highest
signal number currently defined. This value changes as the user selects options and enters values for
the size of enumerated signal sets. This value is also affected when the user changes the value of the
symbol’s offset. If any of these actions would place the highest digital signal above 4095 or the
highest non-digital signal above 1023, the text box containing the highest signal number turns red to
alert the user. The user must bring the signals within range before attempting to activate the signal
block or an error is added to the server log. Also note that when attempting to start the server
protocol, an error is reported if any
Intersystem Communication
symbols sharing the same
connection have signal ranges that overlap.
Large configurations are often not able to fit all their signal blocks within this space.
TCP/IP connections use a Virtual COM port which offers 128 discrete channels. For
such connections, each channel supports a separate i/o stream, and hence a separate
signal space. The solution is to apportion your signal blocks among a number of
channels. For RS-232 connections, there is only the one channel with which to work.
In such cases, a second physical connection is needed.
The following sections discuss different connection models in detail.
One Connection, Many Signal Blocks
Signal Blocks configured in the server for a particular control system can “talk” to
their respective
Intersystem Communications
symbols through a single connection
