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SC 2000, SC2001, SC3004
Chapter 7 Serial Communications
7.1 Overview
The SC Series instruments are designed to communicate with a
remote computer system or terminal for the purpose of transfer-
ring data values from the instrument to the remote system. The re-
mote computer or terminal also can control many of the functions
performed by the instrument.
This chapter is a brief introduction to serial communications with
SC Series instruments. A separate instruction manual is available
to assist with the hookup and wiring for data communications as
well as provide detailed information of all the available com-
mands. Ask for manual 008-0610-00, "SC Series Communica-
tions Guide" or download it from http://measurementsensors.
honeywell.com.
7.2 Wiring
The System connector on the instrument's rear panel is used,
among other things, for serial communications. See "System Con-
nector" on page 17 for wiring information.
All of the serial communications pins on the 25-pin System con-
nector have 500 V of electrical isolation from all other pins and
connectors on the instrument. Additionally, all serial communica-
tions pins are protected against electrostatic discharge (ESD).
7.3 Communications Protocol
7.3.1 RS-232 vs. RS-485
SC Series instruments are available with either of two communi-
cations protocols, RS-232 or RS-485. Only one of these can be
installed at a time at the factory.
•
RS-232 provides for only one receiver and transmitter per
loop, and a loop length of no more than 50 feet.
•
RS-485 allows up to 32 devices per loop, and a loop length
of no more than 4000 feet. All devices receive messages
in parallel on the line, the so-called "multi-drop" system.
To avoid garbled transmissions, only one device should
respond to a particular message. Therefore, every device on
the loop must have a unique address.
If you have an instrument with more than one channel, transmis-
sion must be addressed to the appropriate channel within the
instrument.
7.3.2 Parameters
All SC instruments use no parity, 8 data bits, and 1 stop bits
("N,8,1") for serial communications. Baud rates available are 300,
600, 1200, 2400, 4800, 9600, 19200 and 38400. As shipped
from the factory, all instruments are set at 9600 baud. The baud
rate can be selected though the front panel.
7.4 Serial Com Menu
7.4.1 Overview
The Serial Com menu allows you to examine and change the
settings for serial communications as well as test the communica-
tions link.
Detailed instructions on operating the SC instrument in the SET-
UP Menu mode can be found in "SETUP Menu mode" on page 7.
A diagram of all menus is located in "Setup Menu Reference" on
page 77.
7.4.2 INTERFACE Menu Item
This menu item indicates which serial communications interface
is installed in the instrument: "RS-232" or "RS-485".
7.4.3. ADDRESS Menu Item
This allows you to examine and change the two-character ad-
dress that the instrument will respond to. The default address of
"00" (ASCII codes decimal 30, decimal 30).
7.4.4. BAUD RATE Menu Item
This allows you to examine and change the baud rate that the
instrument uses for serial communications. The default baud rate
is 9600.
7.4.5 AUTO LINE-FEED Menu Item
This allows you to examine the setting (on/off) of the auto line-
feed function. When set to "on", a line-feed character (ASCII
code decimal 10) is transmitted just before the carriage return
(ASCII code decimal 13) that signifies the end of the instrument's
response.
If the instrument is connected to a dumb terminal or printer,
inserting a line feed before the carriage return will make each
message sent by the instrument appear on a separate line and
thus be easier to read.
The default setting is "on".
008-0608-00
Rev. G,
Honeywell Sensing and Control
21
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