13.2 Metasys N2

•The gateway acts as a Johnson Controls Metasys N2 slave, and supports N2 analog input, analog output, binary input and binary output object types.

•Analog input (AI) objects are used for monitoring analog status items. AI objects support low alarm limits, low warning limits, high warning limits, high alarm limits and differential values. Change of state (COS), alarm and warning functions can also be enabled. An AI object will accept an override command, but will not change its actual value or indicate override active. A “multiplier value” is associated with the object, and is multiplied to the point’s value to produce the floating-point AI value sent to the NCU (AI value = [point data value] X multiplier).

•Analog output (AO) objects are used for setting and monitoring analog control and configuration items. An AO value can be modified by issuing an override command. Issuing a release command will not cause the AO to automatically return to its pre-override value, nor will the AO automatically return to its pre-override value after a certain time period of no communication. A “multiplier value” is associated with the object, and the floating-point AO value is divided by this multiplier to produce the result that is passed on to a point’s value (point data value = [AO value] / multiplier).

•Binary input (BI) objects are used for monitoring discrete (digital) status items. BI objects support COS, alarm enabling and normal/alarm status indications. A BI object will accept an override command, but will not change its actual value or indicate override active. A “bit mask” is associated with the object, and is used to determine the current state of the BI by inspecting the point’s data at the bit location(s) indicated in the bit mask. If all of the bit locations of the point’s data value indicated by a “1” in the bit mask are set, then the BI’s current state is set to “1”. Else, it is set to “0”. The point data’s least-significant bit (LSB) is bit #0, and the most- significant bit (MSB) is bit #15.

•Binary output (BO) points are used for setting and monitoring discrete control and configuration items. A BO value can be modified by issuing an override command. Issuing a release command will not cause the BO to automatically return to its pre-override value, nor will the BO return to its pre-override value after a certain time period of no communication. A “bit mask” is associated with the object, and is used to determine the current state of the BO by modifying the point’s data at the bit location(s) indicated in the bit mask. When the BO’s current state is set to “1” by the NCU, then the bit(s) of the point’s data indicated by a “1” in the bit mask are set. Similarly, when the BO’s current state is set to “0” by the NCU, then the bit(s) of the point’s data indicated by a “1” in the bit mask are cleared. The point data’s least-significant bit (LSB) is bit #0, and the most-significant bit (MSB) is bit #15.

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