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Simrad MX500 | 179

threshold and may be the cause of interface problems. If

this is the case, try using an RS-232 to RS-422 convertor

to interface with the MX500. This may more likely solve

the problem. Otherwise third party conversion boxes

may be necessary.

Cables provided for the NMEA signals are shielded pairs.

If extension cables are needed, be sure to use similar

shielded pair cables in order to avoid spurious signal ra-

diation. More than one NMEA listener can be connected in

parallel to the same NMEA talker. The maximum number

of listeners connected to a single talker is dependent on

the combined listener input impedance’s, and the capac-

ity available for data throughput.

MX500 NMEA 0183 Sentences

The NMEA Standard provides for asynchronous transmis-

sion, with a single Talker and multiple Listeners per line.

Typical use includes information transfer from electronic

positioning and navigational devices to autopilots, plot-

ters, terminals, printers, etc.

The NMEA 0183 Standard uses an 8 bit ASCII block

oriented protocol, that is not compatible with the NMEA

0180 simple format or the NMEA 0182 complex format

due to differences in data format, baud rate and parity

bits.

Data Format

Data are transmitted in different sentences, each con-

taining one or more data fields. A field consists of a

string of characters immediately preceded by a “,”

(comma) character, except for the first (address) field

which is preceded by “$”, indicating the beginning of a

new record. Hex 0D 0A <CR>< LF> - end of sentence -

must follow the last field in each sentence.

The data fields are identified only by their position within

the sentence as determined by the field delimiters (com-

ma). Numerical data fields within a sentence may vary in

length from one sentence to another, depending on the

precision available.

Data field position is therefore determined only by count-

ing “,” (commas) rather than counting the total number

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Memorex RX 1 Smart Installationshandbuch Seite 180