Instruction Manual
748441-D
April 2002
Rosemount Analytical Inc. A Division of Emerson Process Management
Serial Interface Option 4-1
Model CAT100
SECTION 4
SERIAL INTERFACE OPTION
4-1 OVERVIEW
The CAT 100 analyzer can be equipped with
a serial interface, enabling communication
with a host computer. The host computer can
read and alter parameters, as well as initiate
analyzer operations, using standardized pro-
tocols. The option BSI circuit board consti-
tutes the hardware interface. This can be
configured as RS 232 C or as RS 485. The
RS 485 interface permits the networking of
several analyzers. Each analyzer may then be
addressed using an assigned numerical ID
code.
Communications are always initiated by the
host computer. Thus, the analyzer is a pas-
sive device whereby the host requests infor-
mation or takes an action such as changing
parameters.
Communications between the host computer
and the analyzer(s) is carried out with the
transmission of a character string containing a
specific syntax. The string always starts with
the “$” (start character), immediately followed
by a three-digit instruction code. Subsequent
elements of the string are separated by the “:”
hyphen character. The final element of all
strings must be the “CR” carriage return char-
acter (terminate character).
Upon receipt of the terminate character, the
analyzer attempts to evaluate the current con-
tents of its input buffer as a valid string. If the
syntax of the transmitted string is correct, the
analyzer will transmit a response string to the
host computer. This consists of the start char-
acter, an instruction code, requested data, a
block-parity byte, and the termination charac-
ter.
If the syntax of the transmitted string was not
correct, the analyzer will transmit to the host
computer a status string containing an error
message. Each terminate character receipt
thus initiates an analyzer response.
To avoid detecting transmission errors, the
host computer can inset a message-length
parity byte immediately preceding the termi-
nate character for verification by the analyzer.
The analyzer always transmits message-
length parity bytes immediately preceding
termination characters.
The elapsed time between reception of start
characters and termination characters is not
limited by the analyzer; i.e., there is no time-
out period.
If the host computer transmits any new char-
acters before the analyzer has responded to
the preceding string, the analyzer’s input
buffer will reject them; i.e., these characters
will be ignored by the analyzer. The analyzer
software is configured such that strings may
be sent to the host computer at time intervals
of 150 ms or greater.
The transmission rate may be set between
600 and 4800 baud.
An echo-mode may also be activated.
