Memorex RX 1 Smart Manual de instalación descargar pdf (Pagina 107)

Installation | 105

The minimum output voltage may be as low as ±2 volt. This is not compatible with

the former 4 volt input 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 MX510. 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 radiation.

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 capacity available for data throughput.

MX51x NMEA 0183 Sentences

The NMEA Standard provides for asynchronous transmission, with a single Talker and

multiple Listeners per line. Typical use includes information transfer from electronic

positioning and navigational devices to autopilots, plotters, 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 containing 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 (comma). 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 counting “,” (commas) rather than

counting the total number of characters from the beginning of the sentence.

The last data field is not followed by a comma delimiter. When a checksum is used, the

last data field is followed by an asterisk “*”, indicating that the checksum follows. The

checksum is the absolute value calculated by exclusive -OR’ing the 8 data bits (no start

bits or stop bits) of each character in the sentence between, but excluding “$” and “*”.

The hexadecimal value of the most significant and least significant 4 bits of the result

are converted to two ASCII characters (0- 9, A- F) for transmission. The most significant

character is transmitted first.

Example:

1 2 ... 102 103 104 105 106 107 108 109 110 111 112 ... 199 200

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Memorex RX 1 Smart Manual de instalación Pagina 107