Matrix Orbital LCD/VFD Legacy - Manual (Page 12)

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, least significant bit, LSB or Low Order Bit of the 8bit address is 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;
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2.2 General Purpose Output
The display has one general purpose output. This is provided to control relays or other electronic devices,
and allows external devices to be turned on or off using the PC or controller and software commands. The
+ terminal is connected to the module positive supply, the - terminal is connected through a 240ohm current
limiting resistor and the electronic switch to ground.
Figure 12: General Purpose Output
Maximum allowable current is 20mA, which is enforced by the current limiting resistor. If the device
being switched has a resistance of 240ohms or more the corresponding resistor may be shorted.
NOTE The GPOs do not have any over current or over / under voltage protection so care
must be taken when using them. For instance if the external device is a relay it must be
fully clamped (using a diode and capacitor) to absorb any generated back electro-motive
force (EMF).
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