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. The display has built in flow control which may be useful when long strings of text are downloaded to
the display. Flow control is enabled or disabled by two commands. If flow control is enabled, the display
will return an "almost full" message (0xFE) to the controller when its internal buffer fills to a defined level,
and an "almost empty" message (0xFF) when the buffer contents drop to a defined level.
4.1.1 I
2
C Communication
The GLC25064 is capable of communicating at 400 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 2.3 and ensure that pull up resistors, with a nominal value of 1K to
10K, are placed on the SCL SDA communication lines coming from pins two and three of the Data / Power
Connector respectively. The GLK24064-25 uses 8-bit addressing, with the 8th 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, to change the I
2
C address see
section 8.2.1.
When communicatingin I
2
C the GLK24064-25will send anACK on the9th clock cycle whenaddressed.
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.
4.1.2 Serial Communication
In addition to being able to communicate via I
2
C the GLK24064-25 communicates natively through the
RS-232 protocol at a default baud rate of 19,200 bps and is capable of standard baud rates from 9600 to
115200 bps. Furthermore the GLK24064-25 is also capable of reproducing any non-standard baud rate in
between using values entered into our baud rate generation algorithm and set through command 164 (0xA4).
The display module communicates at standard voltage levels of . at ±12V to ±12V or at TTL levels of 0 to
+5V by setting the Protocol Select Jumpers to TTL.
Matrix Orbital GLK24064-25 15
