Watkins-Johnson Company WJ-8711A, Installation, Operation And Maintenance Manual

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RS-232 REMOTE OPERATION WJ-8711A DIGITAL HF RECEIVER
4-2
This section of the manual contains all the information necessary to enable an operator to
control and monitor the above receiver parameters from an RS-232 controller. Details on how to properly
format and transmit remote messages and how to read responses from the receiver are provided.
Before attempting to operate the receiver remotely, it is recommended that the operator
become familiar with the operation and capabilities of the receiver by viewing the information provided in
Section III of this manual. It is also recommended that the operator become familiar with the operation of the
controller by viewing its literature.
4.2
INTERFACING WITH THE WJ-8711A
The RS-232 interface of the WJ-8711A is physically implemented on the RS-232 connector
(A2J3), located on the rear panel. This interface has a full duplex operation, meaning that it can transmit and
receive data simultaneously. The interface is set up as a "three-wire" RS-232 configuration, implemented on
the transmit data line (TXD), the receive data line (RXD), and ground. These three wires are provided at the
rear panel RS-232 connector on pins 2, 3, and 7, respectively.
This interface supports software handshaking only, including XON/XOFF (receiver protocol)
and ACK/NAK (transmitter protocol). Hardware handshake signals such as RTS (request to send), CTS (clear
to send), DTR (data terminal ready), or DSR (data set ready) are not supported.
RS-232 serial interfaces use a method of transmitting data one bit at a time over the TXD and
RXD lines. For example, an eight-bit character takes eight sequential transmissions to complete the character.
In RS-232 serial transmissions, data is sent in frames (or packets). Each bit within the frame is determined by
a voltage level. The voltage levels used by this interface are -8 Vdc (nominal) for a logic "1" and +8 Vdc
(nominal) for a logic "0". In the inactive or quiet state, the transmit line is held at a logic 1.
The baud rate (rate of data flow in bits per second) for the WJ-8711A is selectable (75, 150,
300, 600, 1200, 2400, 4800, or 9600 bps). Refer to
paragraph 3.10
for details on selecting the baud rate with
the SPECIAL FUNCTION key. Switches 1, 2, and 3 of DIP switch A2S1 can be set to appropriate positions
to select the hardware default baud rate. Refer to
paragraph 2.2.5 in Section II of this manual for details on
configuring DIP switch A2S1.
The WJ-8711A is set up with a fixed data word frame format consisting of ten bits, and
comprised of the following:
•
one start bit,
•
an eight-bit character, and
•
one stop bit.
It is important in serial data transmissions that the receiving device knows when data is being
transferred and when data being transferred is about to stop. This information is conveyed by the above start
and stop bits. The start bit synchronizes the receiving device so it reads the data properly. The stop bit
notifies the receiving device that the data frame has ended. The WJ-8711A's fixed data word frame format
does not contain a parity bit.
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