LCD0821 rev 2
12
The LCD0821 uses a standard Phillips 7bit address as defined by Phillips. How ever, we at Matrix Orbital
specify I
2
C address in 8bits. The 8
th
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. If one adds the read write bit to this 7bit address and you assume that you are writing one gets
10001010. Matrix Orbital would describe the Philips 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
2.2 General Purpose Output
The LCD0821 has a general purpose output which can be used to control relays or other electronic devices.
This allows external devices to be turned on or off using your PC or controller and software commands.
(See sections 5.1.5 and 5.1.6 for the command syntax.)
The output is wired as shown in Figure 2-. The + terminal is connected to the module positive supply, the –
terminal is connected through a 240 ohm current limiting resistor and the electronic switch to ground.
+ 5 VDC
240 ohm current limiting resistor
load
+
-
Figure 2-10 General Purpose Outputs
Maximum allowable current is 20 mA, which is enforced by the current limiting resistor. If the device being
switched has a resistance of 240 ohms or more the corresponding resistor may be shorted. Solder a small
jumper wire (wirewrap wire is good) between the two feedthrough holes as shown in Figure 2-11.
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