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RS-232 Programmer’s Reference Ultra-Cool
36 Rev 008, 01/12
© SP Scientific 2012
Transmitted Data
It is anticipated that in a remote controlled operation of the target system, the actual
controlling "device" may be either a computer with a software program, or a human
being working interactively. The format of returned data has been optimized for
evaluation by a computer program, although it can be intelligently read by a human
working in an interactive mode.
The content of transmitted data to the host is dependent upon the type of received
data to which the system is answering. The returned message consists of one or more
segments:
Acknowledge: receipt and acceptance of a message which is syntactically 1.
correct, meets all constraints or limits imposed by the system, and which has
been subsequently processed, is acknowledged by the character string "OK".
Note: Certain absolute commands may result in a “runtime” error (in other words, will
result in an error when the software attempts to actually execute the statement). These
will result in both “OK” and the error message described next.
Error Message: receipt of a message that is syntactically incorrect, exceeds 2.
system limits, or is otherwise faulty (such as Parity Error), will result
alternately in an error message.
Parameter Message: in response to a query, the parameter and its value will 3.
be returned to the host. If multiple value/status queries are transmitted in a
single statement, the multiple replies will be transmitted on multiple lines (
i.e .,
separated by carriage returns).
Terminator Character: All messages will be terminated by an exclamation 4.
point ("!") (ASCII 033 decimal / 21 hex). This character is appended to a
single-line message, including "OK", or to the end of the last line of a multiline
message if the host has transmitted queries.
The controller is capable of "full duplex" operation; i.e ., it is capable of 5.
receiving data while transmitting data. However, it is strongly suggested that
the host wait for the message “OK” and the exclamation point ("!") before
proceeding to its next transmission, to ensure correlation between information
sent and the replies.
The Command POLL has been provided as a non-operative command (similar
to an assembly language NOP or BASIC language REM) to verify
establishment of communications between the host and the slave. The POLL
command will have no effect on the state of the controller or its system, and
can result in an error only if the RS-232 connection itself is not correct (
e.g
.,
wrong BAUD rate, parity error,
etc
.).
Once the POLL command has been issued, and the string "OK!" has been received
by the host, the software may be assumed to be synchronized.
User software should be configured to transmit a message (received data), receive
the reply (transmitted data), and verify the integrity of the exchange before proceeding
to the next transmission.