Matrix Orbital GLK12232-25-SM Legacy - Manual (Page 11)

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Now the unit will be able to communicate over I2C. It uses the same pins as RS232.
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 you might be familiar with (i.e. memory chips, etc…)
is that the Matrix Orbital module employs a microprocessor 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 LK404-55 uses a standard Phillips 7bit address as defined by Phillips. How ever, we at Matrix Orbital
specify I2C 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. 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 I2C address of 45hex as 8Ahex. The read address
would be 8Bhex. Much more detail on this basic I²C function can be found in the I²C specification by
Philips. A good reference is also available at...
http://www.ping.be/~ping0751/i2cfaq/i2cindex.htm
2.2 General Purpose Outputs
The GLK12232-25-SM has two general purpose outputs, G1 and G2. These are provided 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 7.1.6 and 7.1.7 for the command syntax.)
The two outputs differ slightly in specification:
G1 provides an output which is switched LOW when ON. When G1 is OFF it is pulled up to +5V
through 150 kohms, in other words it can only be used to "ground" an external device. Maximum
current is 250 mA.
G2 provides an output which is switched LOW when ON. When G2 is OFF it is pulled up to +5V,
supplied by the module. Maximum current is 250 mA.
Both outputs are referenced to ground.
Typical use of these outputs is shown in Figure 2-2.