Matrix Orbital GLK12232-25-FGW - Manual (Page 19)

• 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 configure data flow on the RS232/TTL and I 2 C
port.
4.1.1 I 2 C Communication Summary
The GLK12232-25 is capable of communicating at 100 Kbps 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 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
Significant 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 /
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 I
2 C 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 filled, or the module is too busy processing data it will
respond with a NAK. When performing a multiple byte read within one I
2 C 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:
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