WJ-8711A DIGITAL HF RECEIVER
RS-232 REMOTE OPERATION
4-27
4.8.2
ENQ/ACK PROTOCOL
When the ENQ character is sent to the WJ-8711A, it responds to a valid message with an
ACK, or to an invalid message with a NAK. An invalid message is indicated on a data communications error
such as framing, noise, or overrun. The transmission of a NAK indicates that one or more of the bytes
received after the last ENQ has a communications error. The ACK/NAK response is only sent after the unit
has completed processing any previous messages in the input buffer and has output any response necessary.
See Table 4-7.
WJ-8711A internally maintains a communications error flag. The flag is cleared on power-up
or the transmission of a NAK. The flag is set when a byte is received with a data communications error.
Upon receiving an ENQ character, the unit responds with an ACK/NAK based on the condition of the
communications flag, after any pending input and output operations are complete.
4.8.3
BUFFER HANDLING
4.8.3.1
Input Buffer
The input buffer is handled in circular fashion allowing simultaneous inputting and processing
of data. The input buffer accepts up to 1024 bytes before overflowing. As data in the buffer is being
processed, additional inputs can be accepted by the unit. Upon receiving a terminator character, the WJ-
8711A processes any previous messages in the buffer. When the buffer has less than 16 unused bytes, XOFF
is generated. XON is generated when the buffer has less than 16 bytes remaining to be processed.
The input buffer processing starts on the receipt of a terminator (LF). If the communications
error flag is set, the buffer contents from the end of the last processed message thru the message terminator is
discarded. In the event the buffer is overrun, its contents are discarded. Messages such as XON, XOFF, and
ENQ have immediate actions. These commands are processed on receipt and are not buffered. All other
incoming data is buffered and processed in the order in which it was received.
4.8.3.2
Output Buffer
The output buffer is handled in circular fashion allowing simultaneous additions and
outputting. The transmission of XON/XOFF has priority over data in the output buffer that is awaiting
transmission. The ACK/NAK transmission are buffered operations so they stay in time synchronization with
query operations. The output buffer holds up to 1024 bytes of data.
Courtesy of http://BlackRadios.terryo.org
Содержание WJ-8711A
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