Computer Interface; Cif Hardware Configuration - CPI 0102324500rR Manual

CHPA S
ERIES

3.6 Computer Interface

The Computer Interface (CIF) port is used to control and monitor the CHPA from an external
data terminal or computer with software provided by the user. The CIF port can be configured
to either RS-232 or RS-422/485 (4-wire) serial hardware format. Using the RS-422/485 serial
hardware format allows an addressable multipoint buss to be implemented, providing serial
communications between a computer and up to 16 other RS-422/485 equipped devices.
Serial format selection is made via a slide switch located inside the unit. To change serial
format, first ensure that prime power is not being applied to the CHPA. Next, remove the
CHPA cover and move the internal slide switch to select the desired format. Refer to Figure 3-2.
The software aspect of the CIF port encompasses two standard protocol formats and a
thorough command set. Protocol format and other serial port parameters, such as baud rate, are
configured through the front panel (CIF Configuration menu). The command set includes all
commands and status essential for operating the CHPA. Using the protocol and command set
described later in this section, users can write software for their own computers.
The serial protocol can be factory configured to match that of the lower power (350/400W)
CHPA, so that software drivers need not be re-written for the higher power (600/700W) CHPA.
This accomplished by setting DIP Switch S1 - Switch #2 of the control Interface CCA to the ON
position. Note that there are slight format differences in the attenuator setting and query
commands. Refer to Table 3-7 and 3-8. Also note that DIP switch setting changes do not take
effect until power to the CHPA has been cycled OFF and ON.
3.6.1

CIF Hardware Configuration

The serial interface can be configured to one of two serial hardware formats: RS-232 or RS-
422/485 (4-wire). A slide switch mounted inside the unit is used to select the hardware format.
The RS-232 serial hardware format is suitable for point-to-point communications over short
distances (50 ft. or 15 m). The RS-422/485 (4-wire) serial hardware format is suitable for either
point-to-point or multi-drop applications over long distances (4000 ft. or 1200 m) provided that
a suitable serial cable is used. Several cable manufacturers offer serial cables specifically
designed for long-distance serial communications applications. For EMI considerations, the
cable shield should be directly attached to the connector shell.
In the multi-drop configuration, up to 16 other addressable RS-422/485 equipped devices may
share the same serial buss. Termination resistors should be installed on the last device on the
buss. If the buss has multiple runs, the terminating resistor should be engaged on the last device
at the end of each run. The CHPA comes from the factory with the CIF termination resistor
disengaged. On the CHPA, the CIF port terminating resistor is installed by turning "ON"
switch 4. Instructions for changing this switch can be found earlier in this chapter under "Serial
Remote Interface." Refer to Figure 3-1 as well.
The CHPA CIF (Computer Interface) is located at connector J7 at the rear panel of the CHPA. It
is a 9-pin D-type connector, with pin assignments as shown in Table 3-5. A computer may be
connected to the connector using the standard RS-422/485 configuration.
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