User guide

Printer Communication Interfaces
A.2 The Serial Port
• Emergency Upper Level = 64
• Lower Level = 256
Input buffer sizes are listed in Table A–1.
Table A–1 Input Buffer Values
LA75 Companion
Printer LA310 MultiPrinter LA600 MultiPrinter
Small 8K 16K 1K
1
8K
1
16K
1
32K
1
Large
1
32K 32K 47K
2
1
Select this feature through setup.
2
This value is the default.
XON/XOFF Control
While XON/XOFF is enabled, DTR remains high. Data flow control is then
achieved as follows:
• When just powered up and ready, the printer sends one XON character to
signal to the data source that transmission may begin.
• When the number of characters in the input buffer reaches the upper
threshold, the printer sends an XOFF character, signaling the data source
to stop transmitting.
• When the number of characters in the input buffer falls to the lower
threshold, the printer sends the XON character to signal that transmission
may resume.
• If the first XOFF character from the printer is missed by the data source
and the input buffer continues to fill, a second XOFF character is sent
when the input buffer fills to its emergency upper threshold.
No special action occurs with XON/XOFF (or XON/XOFF + DTR for the
LA600 printer) in the event of an error condition such as ‘‘out of paper’’ or
‘‘cover open.’’ XOFF is sent as usual after the input buffer reaches the upper
threshold.
Similarly, the printer does not send XON after the error condition is corrected
until the input buffer reaches the lower threshold.
Printer Communication Interfaces A–3