Watkins-Johnson Company WJ-8711A, Инструкция по установке, эксплуатации и обслуживанию

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CSMA REMOTE CONTROL WJ-8711A DIGITAL HF RECEIVER
5-4
5.5
SERIAL DATA TRANSMISSIONS
Data in serial transmissions is read from the transition of the change in state (i.e., high to low,
or low to high). Data transmitters and data receivers connected on the interface exchange serial information
using the NonReturn to Zero (NRZ) format. This means, in baseband transmissions, if a logic "1" is
continuously sent, the signal does not return to logic "0" until a logic "0" is sent. The composition of one byte
of data is shown in
Figure 5-2
with an example of the NRZ format.
87IL8
H
L
START
BIT
BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 STOP
BIT
1 1 1 0 0 1 1 0 1
IF THE "1" IS SENT
CONTINOUSLY, THE
SIGNAL DOES NOT
RETURN TO "0" LEVEL.
Figure 5-2. Composition of One byte of Serial Data
5.6
COMMAND MESSAGE FORMATTING
The typical message format of a command packet used with this interface is provided in
Figure 5-3
. Each block in the packet contains one byte of data. As shown in the figure the packet consists of
two preamble bytes, a receiving station address byte, a transmitting station address byte, a control code byte, a
varying number of data bytes, and an end of message byte. All information contained in bytes is expressed in
hexadecimal except for the data bytes which may vary in number and are expressed in packed binary coded
decimal (BCD).
FE
PREAMBLE
FE
RX
ADDR
TX
ADDR
CONTROL
CODE
DATA BYTES
(VARIABLE IN NUMBER)
END OF
MESSAGE
FD
87IL9
Figure 5-3. Format of Typical Command Message Packet
Courtesy of http://BlackRadios.terryo.org