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

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WJ-8711A DIGITAL HF RECEIVER CSMA REMOTE CONTROL
5-5
The preamble [FE|FE] identifies the start of a message. The receiver address (RX ADDR)
identifies the address of the unit that is to receive the data. The WJ-8711A's address setting should be entered
at this location. The transmitting station address identifies the address of the controller sending the data. The
control code represents the WJ-8711A function that is to be controlled. This code should always be sent in
hexadecimal format. The variable length data field contains data that accompanies the control code to set
certain values of the function. This data field can contain any number of bytes required to send the data. Data
in these bytes should always be sent in binary coded decimal format. The end of message byte [FD] identifies
the end of the message being transmitted.
5.7
CONTROL CODES
Table 5-1 lists the control codes used for controlling the receiver functions. The control
codes listed are shown in hexadecimal format. A description is provided for each control code. Data
accompanying control codes is shown in decimal format unless otherwise noted.
Certain control codes require that an acknowledgment be sent to the host controller indicating
that their format was valid and accepted. For all control codes that require an acknowledgment, hexadecimal
FB (ACK) is returned to the controller when the control code is recognized and the accompanying data is
within the specified range. Hexadecimal FA (NAK) is returned to the controller if either the control code sent
is unsupported or if the accompanying data sent with a supported control code is out of range. Note that
unless otherwise indicated the control code requires an acknowledge.
Figure 5-4
shows the format of ACK
and NAK responses.
FE
PREAMBLE
FE
RX
ADDR
ACK
CODE
END OF
MESSAGE
1A F1 FB FD
CNTRL
ADDR
ACKNOWLEDGE (ACK)
MESSAGE
FE
PREAMBLE
FE
CNTRL
ADDR
RX
ADDR
NAK
CODE
END OF
MESSAGE
1A F1 FA FD
95-1341
NOT ACKNOWLEDGE (NAK)
MESSAGE
Figure 5-4. Format of ACK and NAK Messages
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