Welch Allyn Scanteam 3000-X2, Руководство по программному меню

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SCANTEAM 3000/PDF Information/Examples RS–232
Baud Rate
This programming selection sets the baud rate from 600 bits per second to 38,400 bits per
second. Programming baud rate causes the data to be sent at the specified rate. Default =
9600 bits per second.
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Character Format
This programming selection allows you to set the character format for number of data and
parity bits. PDF capable products support seven or eight bits of data and zero or one parity
bit per character. The number of start and stop bits is fixed at one each. If an application
requires only ASCII characters 0 through 127 decimal (text, digits, and punctuation), select
7 data bits. For applications requiring use of the full ASCII set, select 8 data bits per
character. Default = eight data bits, no parity, and one stop bit.
Data Flow Control
Note: PDF417 data is checked for accuracy before it is transmitted. This doesn’t
guarantee that errors won’t be introduced during data communication. A parity bit may be
added to each transmitted character as a means of character validation. A checksum
character may also added to the message as a postamble (suffix), for even stronger
security (see Preamble/Postamble menu page). The receiving device must be set up for
precisely the same character format as the reader, to ensure reliable communication.
Flow control may be necessary to handle the larger PDF417 messages. The PDF417
reader will normally transmit a message immediately following a successful decode. With
flow control selected, the receiver can enable/disable the reader’s transmitter. Default =
“None,” no data flow control option selected.
For example: suppose the receiver stores transmitted characters in a 512–byte buffer, yet
the PDF417 reader has a 1400–byte message to transmit. The receiver might take 510
characters into its buffer, then tell the reader to STOP transmitting. As the receiver
processes the message, space becomes available in the 512–byte buffer and the receiver
can tell the reader to START transmitting again.
Two methods of flow control have been implemented in the PDF capable products:
RTS/CTS hardware handshaking, and an XON/XOFF protocol.
RTS/CTS Handshaking
This option will use two wires connected to both the reader and the receiver. The reader will
have control of the RTS line, the receiver controls the CTS line.
Whenever the reader has a message to send, it will raise (the voltage on) the Ready To
Send (RTS) line. (If the reader has no messages to send it will ground the RTS line.) When
the receiver wants to suspend transmission it should ground the CTS line. The reader
looks at the state of CTS prior to sending each character. When the receiver is willing to
accept a message from the reader it should raise (the voltage on) the Clear To Send (CTS)
line. The reader will resume sending messages, continuing where it left off when the CTS
line was grounded.
XON/XOFF Protocol
This option uses only the transmit/receive lines between the reader and the receiver.
When the receiver wants to suspend transmission, it will send the XOFF character (ASCII
19 decimal) to the reader. When the receiver wants to resume transmission, it will send the
XON character (ASCII 17 decimal) to the reader. The reader will resume sending
messages, continuing where it left off when the XOFF character was sent.