?
Third, please ensure that the display module's memory is not
full. The GLK12232-25 has 16 Kb of
memory for fonts and bitmaps.
NOTE
If you are unable to resolve any issue please contact Matrix Orbital. See
16.5 on
page 61
for contact information.
4 Communications
4.1 Introduction
The commands listed in this chapter describe how to con?gure
data ?ow on the RS232/TTL and I
2C
port.
4.1.1 I2C Communication Summary
The GLK12232-25 is capable of communicating at 100 Kbps in I2C mode, with 127 units addressable on
a single I2C communication line. However, in order to communicate via I2C you must ?rst set the Protocol
Select Jumpers as can be seen in
Section 2.4
and 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. These pins are shared with RS232 and must be switched to I2C if this is how
the host will be communicating with the display. 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. The GLK12232-25 uses 8-bit addressing, with the 8th or Least
Signi?cant 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 modulewill be 0x51, whereas the write address is 0x50
by default. This address may be changed by using cmd 254 / 51 / <address>. The GLK12232-25should 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 GLK12232-25, 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 GLK12232-25 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 GLK12232-25 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
that the transmission is over.
The GLK12232-25 has some speed limitations, especially when run in I2C mode. Here are some con-
siderations when writing I2C code:
Matrix Orbital GLK12232-25
14