3400, 3440, and 3600 Bar Code Label Printer User’s Manual
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NugFont
Code39
C-4
Note: Do not confuse the Buffer now full <DC3> status with the XON/XOFF
characters <DC1> and <DC3>.
When the printer returns Buffer Now Full (<DC3>) status, it accepts the
currently received message block. At this time, the printer can accept short
messages to allow parsing of immediate commands such as Reset (<DLE>) or
Cancel Batch Printing (<EM>). However, if the printer responds with a <GS> to
any message block, the buffer is already full and the printer discards the entire
message block.
XON/XOFF Protocol (Software and Hardware Flow Control)
The XON/XOFF protocol stops the host from sending data when the printer
buffer fills up and starts the host again when the buffer empties. When you
select this protocol, you concurrently enable software and hardware flow
control. Software flow control uses the ASCII characters <DC1> (XON) and
<DC3> (XOFF) to start and stop the flow of data from the host to the printer.
Hardware flow control uses pin 11 or pin 20 (internally connected together) on
the printer’s serial port to indicate “Ready” or “Busy” for data flow control. As
with Standard protocol, <STX> and <ETX> enclose data. Status responses
conform to the table above except that <DC2> is substituted for <DC1> and
<DC4> is substituted for <DC3>.
The printer does not restrict the message length for XON/XOFF protocol. That
is, the printer processes information as it is being downloaded and stops when
there is no more information. There is no restriction on the number of
characters that can be sent down at a time. <STX> and <ETX> are optional
characters.
Pin 11/20 reports “Ready” and a <DC1> (XON) is transmitted when the printer
finishes reloading at power-up. Pin 11/20 reports “Busy” when the printer’s
input buffer fills with 768 bytes of data. If the host ignores pin 11/20 and
continues to transmit data, the printer transmits a <DC3> (XOFF) after
receiving 15 additional characters. The printer continues to transmit a <DC3>
after every 15 characters received if the host continues to transmit data. Data
integrity is not guaranteed if this happens.
Pin 11/20 becomes “Ready” when the printer has transferred all the data from
the input buffer. If the printer receives a <DC3>, it transmits a <DC1> (XON)
and the host may resume transmission. When you switch the printer offline,
pin 11/20 becomes “Busy” and it transmits a <DC3>. When you switch the
printer online (and the input buffer is empty), pin 11/20 becomes “Ready” and
it transmits a DC1.
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