
Cables
Selecting a cable for the RS-232C interface is dependent on your specific
application. The following paragraphs describe which
of the
HP
are used to control the operation of the RS-232C relative
to the HP
To locate the proper cable for your application,
refer to the reference manual for your controller. This manual should
address the exact method your controller uses to operate over the
RS-232C bus.
Minimum
With a three-wire interface, the software (as compared to interface
Three-Wire
Interface with
Software
hardware) controls the data flow between the HP
and the
This provides a much simpler connection between devices
since you can ignore hardware handshake requirements. The
HP
uses the following connections on its RS-232C interface for
Protocol
three-wire communication:
l
Pin 7 SGND (Signal Ground)
l
Pin 2 TD (Transmit Data from HP
l
Pin 3 RD (Receive Data into HP
The TD (Transmit Data) line from the HP
must connect to the
RD (Receive Data)
on the controller. Likewise, the RD
from the
HP
must connect to the TD
on the controller. Internal
pull-up resistors in the HP
assure the DCD, DSR, and CTS
lines remain high when you are using a three-wire interface.
The three-wire interface provides no hardware means to control data flow
between the controller and the HP
protocol is the
means to control this data flow.
Programming Over
3-2
HP
16518
Programming Reference