Section 4 - RS232 Communications
The controller and reference meter provides for bi-directional data transfer via
a three conductor cable consisting of signal ground, receive input, and transmit
output. It is recommended that less than fifty feet of shielded cable be used
between the computer and this instrument. This will assure performance
of the BB705 to EN61326 standards, under the E.M.C. Note that multiple
instruments cannot be tied to the same port in this configuration. The RS232 port
is optically isolated to eliminate ground loop problems.
In Figure 9 is a pinout diagram for the serial port of the BB705 as well as the
pinout for a 9-pin PC serial port. Use a straight DB9 (female) to DB9 (male)
connector cable to connect your computer to the BB705. The cable should be
attached only when the computer and BB705 are off.
Only parameters in the parameter list should be modified or queried via the
serial port. Other parameters should be viewed or queried from the controller,
directly. It is highly recommended that baud rate for the controller be modified
on the controller, directly. Note that both the BB705 and the computer must be
communicating with the same serial communications parameters to establish a
working communication link.
The serial communications feature can be tested using terminal emulation
package. Note that this controller does not time out waiting for the next
character to be transmitted. Be sure not to use the XON/XOFF or hardware
handshaking. Lastly, it should be noted that following a complete transmission
to the BB705, a response it sent back. If the message was valid, the changed or
queried parameter is echoed back (following the same format). If the message
was not according to acceptable format or was attempting to force a parameter
out of range, an “ERROR” message is echoed.
Figure 9. Connecting a PC to the BB705’s Controller/Reference Meter Serial Port
RS232 Communications
4
4-1
1
6
7
8
9
6
7
8
9
2
3
4
5
1
2
3
4
5
RX
TX
GND
TX
RX
GND
BB705
BLACKBODY
CALIBRATOR
(CONTROLLER
OR REFERENCE
METER)
COMPUTER
SERIAL
PORT
(RS232)