Matrix Orbital GLT240128 Legacy - Manual (Page 21)

3.3 The display module is communicating, however text cannot
be displayed.
• The cause of this is often that no font has been loaded onto the display. To load a font onto the display
see Section 4.2.1 on page 16.
• Another common cause may be that the contrast settings have been set to low. The solution to this
problem is to adjust the contrast settings, the default setting that will work in most environments is
128
NOTE Optimal contrast settings may vary according to factors such as temperature, view-
ing angle and lighting conditions.
3.4 There is a problem uploading fonts or bitmaps.
• First, ensure that you can communicate to the display. A good test is to use a PC, with MOGD#
installed, to connect to the display. See Section 1.4 on page 4for setting up a PC to test the GLT240128.
• Second, ensure that the Filesystem Lock Jumper has not been set. See Section 2.7 on page 13.
• Third, please ensure that the display module’s memory is not full. The GLT240128 has 16 Kb of
memory for fonts and bitmaps.
NOTE If you are unable to resolve any issue please contact Matrix Orbital. See 15.6 on
page 64 for contact information.
4 Communications
4.1 Introduction
The commands listed in this chapter describe how to configure data flow on the GLT24064.
4.1.1 I 2 C Communication Summary
The GLT24064 is capable of communicating at 100 KHz in I 2 C mode, with 127 units addressable on a
single I 2 C communication line. However, in order to communicate via I 2 C you must first ensure that pull up
resistors, with a nominal value of 1K to 10K, are placed on the SCL and SDA communication lines coming
from pins two and three of the Data / Power Connector respectively. Data responses by the module are
automatically output via RS232, in case the host will be querying the module, it is necessary for the host
to inform the module that its responses are to be output via I
2 C. This can be done by sending command
254 /160 / 0 to turn off auto transmission of data in RS232. This will keep the data in the buffer until the
master clocks a read of the slave. The I
2 C data lines operate at 5V normally or 3.3V for -1U style units. The
GLT24064 uses 8-bit addressing, with the 8th or Least Significant Bit (LSB) bit designated as the read/write
Matrix Orbital GLT240128 16