Maretron Alarm Module ALM100 Manual de usuario descargar pdf (Pagina 57)

Figure 12 – Setting Instance Number

For simple configurations, where there is only one source of data, N2KView

allows the Instance Number to be set to “Any”. If this is chosen, the component

will lock on to the first matching parameter received on the NMEA2000 bus,

regardless of its Instance Number. If there are more than two matching

parameters on the bus, this will lead to unpredictable behavior. If there is only

one matching parameter, it is an easy way to set up the component without

knowing what the real Instance Number is.

Instance Numbers can either be allocated to the Device as a whole (Device

Instancing) or to individual data elements (Data Instancing).

8.3.1.1 Device Instancing

The device instance is an eight-bit value (ranging between 0 and 255) that every

NMEA 2000 device transmits when it joins the bus and upon request thereafter.

This becomes important when you have multiple devices that transmit the same

data. It is possible, for example, to have two GPS antennas on a vessel, with

one serving as a primary antenna and others serving as backups. If this is so,

the NMEA 2000 standard requires that the two different antennas have two

different device instances. If you are using a certified NMEA 2000 product, the

NMEA 2000 standard requires that a user be able to program the device instance

in each product. Consult the device documentation or contact your device

manufacturer in order to determine how to program the instance into a particular

device.

8.3.1.2 Data Instancing

Certain NMEA messages, such as those from batteries, tanks, engines, and

transmissions, have data instances embedded in the messages. These data

instances are used, if programmed, to relate data to specific data sources. Data

instances are also required by the NMEA 2000 standard to be field-

programmable, so please consult your device’s documentation for details on how

to program this value.

Revision 4.0.2 Page 57

1 2 ... 52 53 54 55 56 57 58 59 60 61 62 ... 379 380

Sin comentarios

Maretron Alarm Module ALM100 Manual de usuario Pagina 57