2.3 I
2
C Communications
I
2
C communications runs at 100Kbps and supports up to 16 units on a single communications line. The
I
2
C data line operates on 5 volt CMOS levels.
2.3.1 ACK
The idea of ACK is to indicate when the data has been received correctly. ACK does not indicate data
incorrectly received. ACK simply fails to indicate when data is correctly received. Clearly, this is of limited
usefulness and even less so with Matrix Orbital modules. Matrix orbital modules are not capable of failing
to acknowledge an incorrectly received byte in response to that bytes transition. They are only capable of
failing to acknowledge the bytes following the byte, which was not received. To fully understand the reasons
for this one needs to understand something about how a Matrix Orbital module processes data. Basically the
reason why a Matrix Orbital module might fail to receive a byte correctly is that it was unable to process the
byte previous before the failed byte was transmitted. Because the module cannot possibly know that it would
be unable to store the byte before the next byte was received it cannot know to not ACK. The reason for this
situation in deference to situations one might be familiar with (i.e., memory chips, etc) is that the Matrix
Orbital module employs a micro-processor to perform these data storage functions. A memory chip takes
care of these things entirely with in hardware subsystems that operate at the same speed as the transmission
themselves.
The display uses a standard Phillips 7bit address as defined by Phillips. However, Matrix Orbital specifies
I
2
C address in 8bits. The 8th bit, or least significant bit, LSB or Low Order Bit of the 8bit address is a read
/ write bit. If we take a standard Phillips 7bit address of 45hex this would be in binary, 1000101. This is
7bits. Matrix Orbital would describe the Phillips I
2
C address of 45hex as 8Ahex. The read address would
be 8Bhex.
For more information on Phillips I
2
C please visit;
http://www.ping.be/~ping0751/i2cfaq/i2cindex.htm
And for more information specific to our displays visit;
http://www.lcdforums.com/forums/viewtopic.phpt=910
To communicate by I
2
C two jumpers have to be set into the I
2
C position above the DB-9 connector.
Figure 14: I
2
C Communications
Connector pinout is as follows;
Matrix Orbital
LCD2041
10
