Preliminary support of pos 'line display' printing

src/escpos/constants.py

@@ -64,6 +64,11 @@ _PANEL_BUTTON = lambda n: ESC + b'c5' + six.int2byte(n)
 PANEL_BUTTON_ON = _PANEL_BUTTON(0)  # enable all panel buttons
 PANEL_BUTTON_OFF = _PANEL_BUTTON(1)  # disable all panel buttons
 
+# Line display printing
+LINE_DISPLAY_OPEN = ESC + b'\x3d\x02'
+LINE_DISPLAY_CLEAR = ESC + b'\x40'
+LINE_DISPLAY_CLOSE = ESC + b'\x3d\x01'
+
 # Sheet modes
 SHEET_SLIP_MODE = ESC + b'\x63\x30\x04'  # slip paper
 SHEET_ROLL_MODE = ESC + b'\x63\x30\x01'  # paper roll

src/escpos/escpos.py

@@ -26,6 +26,7 @@ from .constants import BARCODE_TXT_OFF, BARCODE_TXT_BTH, BARCODE_TXT_ABV, BARCOD
 from .constants import TXT_SIZE, TXT_NORMAL
 from .constants import SET_FONT
 from .constants import LINESPACING_FUNCS, LINESPACING_RESET
+from .constants import LINE_DISPLAY_OPEN, LINE_DISPLAY_CLEAR, LINE_DISPLAY_CLOSE
 from .constants import CD_KICK_DEC_SEQUENCE, CD_KICK_5, CD_KICK_2, PAPER_FULL_CUT, PAPER_PART_CUT
 from .constants import HW_RESET, HW_SELECT, HW_INIT
 from .constants import CTL_VT, CTL_HT, CTL_CR, CTL_FF, CTL_LF, CTL_SET_HT, PANEL_BUTTON_OFF, PANEL_BUTTON_ON
@@ -570,6 +571,41 @@ class Escpos(object):
             except:
                 raise CashDrawerError()
 
+    def linedisplay_select(self, select_display=False):
+        """ Selects the line display or the printer
+
+        This method is used for line displays that are daisy-chained between your computer and printer.
+        If you set `select_display` to true, only the display is selected and if you set it to false,
+        only the printer is selected.
+
+        :param select_display: whether the display should be selected or the printer
+        :type select_display: bool
+        """
+        if select_display:
+            self._raw(LINE_DISPLAY_OPEN)
+        else:
+            self._raw(LINE_DISPLAY_CLOSE)
+
+    def linedisplay_clear(self):
+        """ Clears the line display and resets the cursor
+
+        This method is used for line displays that are daisy-chained between your computer and printer.
+        """
+        self._raw(LINE_DISPLAY_CLEAR)
+
+    def linedisplay(self, text):
+        """
+        Display text on a line display connected to your printer
+
+        You should connect a line display to your printer. You can do this by daisy-chaining
+        the display between your computer and printer.
+        :param text: Text to display
+        """
+        self.linedisplay_select(select_display=True)
+        self.linedisplay_clear()
+        self.text(text)
+        self.linedisplay_select(select_display=False)
+
     def hw(self, hw):
         """ Hardware operations
 

test/test_function_linedisplay.py

@@ -0,0 +1,35 @@
+#!/usr/bin/python
+"""tests for line display
+
+:author: `Patrick Kanzler <patrick.kanzler@fablab.fau.de>`_
+:organization: `python-escpos <https://github.com/python-escpos>`_
+:copyright: Copyright (c) 2017 `python-escpos <https://github.com/python-escpos>`_
+:license: MIT
+"""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
+import escpos.printer as printer
+
+
+def test_function_linedisplay_select_on():
+    """test the linedisplay_select function (activate)"""
+    instance = printer.Dummy()
+    instance.linedisplay_select(select_display=True)
+    assert(instance.output == b'\x1B\x3D\x02')
+
+def test_function_linedisplay_select_off():
+    """test the linedisplay_select function (deactivate)"""
+    instance = printer.Dummy()
+    instance.linedisplay_select(select_display=False)
+    assert(instance.output == b'\x1B\x3D\x01')
+
+def test_function_linedisplay_clear():
+    """test the linedisplay_clear function"""
+    instance = printer.Dummy()
+    instance.linedisplay_clear()
+    assert(instance.output == b'\x1B\x40')
+