Description of RS-485
GENERAL DESCRIPTION OF RS-232
RS-232 serial communications uses fixed voltage
values and generally
allow you to connect to only one device (such as one temperature
These fixed voltage signals are more easily affected by noise and
problems then are the differential signals of RS-485 serial
but with appropriate cabling you can run a cable 10 feet or more.
Our RS-232 interface also includes a protocol
capability so that information
can be sent to, and received from, the attached device. A protocol
the way you encode commands and data for transmission and
The protocol we use for our standard temperature
controllers is unique
to our controllers, and our custom built temperature controllers will
be assigned new, custom protocols based on the requirements of the
Our communications protocols apply to all our computer compatible
controllers regardless of the method of communications (RS-485, RS-232,
For programming information for the protocol of
our standard controllers
see our Communications Protocol
Windows system device properties for
For most of our standard Controllers the
Port Properties' Port
- Bit per Second: 9600
- Data Bits: 8
- Parity: None
- Stop Bits: 1
- Flow Control: None
See your temperature controller's Operators Manual for different
settings required by your controller.
Normally, cable runs are not long and induced
noise is not a problem.
Telephone cable can be used for a cable.
Modular Connection: We can provide a 7
foot, 6 wire telephone
cable with modular connectors on the ends. We can also provide a DB9
for this cable. To connect to the controller, you can either cut off a
connector on one end of the cable and connect with bare wires, or you
use a Radio Shack® Snap-In Module Category 3 Jack, P/N
which has a modular jack on one side and bare wire connectors on the
(bare wire connector #2 goes to the controller's JP3-2, #3 to JP3-1,
#4 to JP3-3).
Off-the-Shelf Cable: You can purchase a
standard RS-232 cable
and make up an appropriate mating connector with short connecting wires
for the controller (connect Tx to Tx, Rx to Rx, and Shield to Common).
Custom Cable: Below are the connections you
use to connect from
a serial communications connector to a controller using the cable and
length of your choice.
The DB9 and DB25
wiring information below
is for our standard controllers, which at the time of this writing
be the 5C7-250, 5C7-251, 5C7-252, 5C7-362 and 5C7-365. For other
check the instructions in your Operators Manual.
DB9: With a DB9 9 pin male
connector for the computer:
DB25: With a DB25 25 pin female connector
for the computer:
- The controller's JP3-1 goes to DB9 pin 3. (Rx
- The controller's JP3-2 goes to DB9 pin 2. (Tx
- The controller's JP3-3 goes to DB9 pin 5.
(Shield to Common)
Cable Specifications: EIA RS-232 specifies:
- The controller's JP3-1 goes to DB25 pin 2.
(Rx to Tx)
- The controller's JP3-2 goes to DB25 pin 3.
(Tx to Rx)
- The controller's JP3-3 goes to DB25 pin 7.
(Shield to Common)
Length: At the 9600 baud communications rate
of our standard temperature
controllers (such as the Models 5C7-250,
5C7-362 and 5C7-365) a properly configured cable can often be run up to
50 feet. A high quality cable may even allow lengths of over 100 feet.
- Cable Configuration: Twisted Pair
- Gauge: 24AWG (24 Gauge)
- Nominal Shunt Capacitance per Foot Between
Conductor Pairs: 15.5 pF
- Nominal Shunt Capacitance per Foot Between a
Conductor and the Shield:
15.5 pF (Picofarrads)
- Nominal Conductor Impedance: 24 Ohms per 1000
- Shield type: Overall braided with drain wire
(see paragraph below)
- Maximum Cable Length: 10 feet when using
56000+ baud serial
rate (see paragraph below)
- Recommended: Approved by Underwriters
Shielded Wire: Troubleshooting an
operational problem that is
due to cabling can be difficult. Since shielded wire is not much more
than unshielded wire, and since it offers improved noise immunity along
the length of the cable, it is best to use shielded twisted pair (STP)
wire for the cable. Connect the shield to the "Shield" connection of
controller, but if your controller does not have a shield connection
at least make sure the shield of the loop is connected from one section
of cable to the next. Your computer's RS-232 serial port, or your
converter, should also have a shield connection marked "Common Ground"
(C or GND) or "Shield".
On the Bench: For testing/setup with very
short runs (a couple
of feet max) on a bench just about any wire can probably be used.
with our standard temperature controllers, you will find it is easier
work with solid copper wire (similar to Radio Shack® 24 Gauge,
Rainbow Wire, P/N 278-857) simply because it is easier to use with the
euro style screw down connectors on the controllers. If you start
for noise immunity, make sure the cable is up to spec.
If communications is not working properly check
all the connections.
Then check the following (note that a Comm port is a serial communications
port on your computer):
For a Comm Port Timeout:
For a Comm Port Open Error: No Comm port is
actually available on
your computer at the Comm port setting you selected.
- No power to controller, or converter (if any).
- Device address is wrong. If you are using a
device address in your
with an RS-232 based controller (as you might from a custom program or
when using a device driver) the address of the controller is one (1).
"universal address" of zero (0) can also be used.
- Wrong Comm port is selected to access from
- Comm port is not really connected to the
device, or to the converter
any), or the converter is not connected to the device.
- Wiring to Comm port of computer, or converter
(if any), or device, is
Power Supply Voltage: Most
controllers need 12 or more
volts (check the specification for your controller). If the power
is not "stiff" enough to support the controller(s) at 12 vdc
will not function properly. A switching power supply rated at 12 vdc
compensate for the draw of the controller in order to maintain 12 vdc.
A linear power supply rated at 12 vdc may dip under 12 vdc when
the circuit board, or when the demand from any load (TEC or heater,
it is powering is to high. (Note that the common "battery eliminator"
generally a linear power supply.)