Matrix Orbital GLK24064-25 Legacy - Manual (Page 16)

care of these things entirely within hardware subsystems which 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 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;
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2.3 General Purpose Output
The general purpose output is provided to control relays or other devices via the display. This allows an
external device to be turned on or off using the controller and software commands.
The GPO is meant to be used as a pair. The positive side of the GPO is connected to a power source of
+5Vdc supplied by the module. This connection is via a 240 ohm resistor which limits the maximum current
to 20 mA. The negative side of the GPO is connected to ground.
If the device which is being driven by a GPO requires a relatively high current (such as a relay) and
has an internal resistance of its own greater than 250 ohms, then the 240 ohm resistor may be removed and
replaced with a jumper. This resistor can be located directly to the left of the positive pin of the general
purpose output.
NOTE This operation requires soldering. With the resistor removed the GPO does not
have any over current or over / under voltage protection so care must be taken when using
the GPO. 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).
Figure 16: Clamping a Relay
Matrix Orbital GLK24064-25 12