3.3 The display module is communicating, however text cannot
be displayed.
?
A 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.
If you are unable to resolve any issue please contact Matrix Orbital. See
12.6 on page 51
for contact information.
4 Communications
4.1 Introduction
The commands listed in this chapter describe how to con?gure
data ?ow on the LCD2041.
4.1.1 I2C Communication Summary
The LCD2041 is capable of communicating at 100 KHz in I2C mode, with 127 units addressable on a
single I2C communication line. However, in order to communicate via I2C you must ?rst 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 I2C. 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 I2C data lines operate at 5V normally or 3.3V for -1U style units. The
LCD2041 uses 8-bit addressing, with the 8th or Least Signi?c
ant Bit (LSB) bit designated as the read/write
bit, a 0 designates a write address and a 1 designates a read address. The default read address of the display
module will be 0x51, whereas the write address is 0x50 by default. This address may be changed by using
cmd 254 / 51 / <address>. The LCD2041 should only be sent addresses that are even (LSB is 0). When the
I2C master wishes to write to the display, the effective address is $50 (0101 0000) , since the LSB has to be
0 for an I2C master write. When the I2C master wishes to read the LCD2041, the effective address is
$51
(0101 0001), since the LSB has to be 1 for an I2C master read.
If we take a standard Phillips 7 bit address of $45 (100 0101),Matrix Orbital's LCD2041 would describe
this Phillips I2C address as $8A (1000 1010). The read address would be $8B (1000 1011).
The unit does not respond to general call address ($00).
When communicating in I2C the LCD2041 will send an ACK on the 9th clock cycle when addressed.
When writing to the display module, the display will respond
with a ACK when the write has successfully
been completed. However if the buffer has been ?lled, or the m
odule is too busy processing data it will
respond with a NAK. When performing a multiple byte read within one I2C transaction, each byte read from
the slave should be followed by an ACK to indicate that the master still needs data, and a NAK to indicate
Matrix Orbital LCD2041
16