VIA Technologies EPIA SN-Series Specifications download pdf (Page 90)

FASTER Engineering Model

6.5.1 Garmin GPS 18 5Hz Acquisition Block

The Garmin GPS 18 5Hz block acquires data packets from the receiver decoding

each sentence and the corresponding Simulink model is shown in Figure 68. For this

specific application only the following sentences were enabled:

 GP-GGA, described in Table 10

 GP-VTG, described in Table 11

 GP-RMC, described in Table 12

 GP-RMV, described in Table 13

The GP suffix indicates that sentences are compliant to the NMEA 0183 standard

[Ref. (49)] but via a proprietary implementation. The transmission time of the entire

subset of enabled sentences, with a 38400 bps serial connection, is 61.18 ms, far below

the maximum allowed time, which at a 5 Hz of refresh rate, is 200 ms.

The Baseboard RS232 Send-Receive FIFO out block is used to get data from one of

the two serial ports and with a First In First Out logic the incoming data is passed to a

FIFO headers reading block which separates the different sentences. Each sentence has a

dedicated decoding block in which the data is read, split into single variables and

converted in double numerical values. Not all the information contained in the sentences

are used thus some are discharged using a terminal block. A cyclic redundancy check is

performed in each decoding block and prevent corrupted data to be propagated inside the

model; in this case decoded data is tagged as not updated and the previous output is

maintained.

A final multiplexer packets the variables in a single GPS vector which constitutes the

block output.

Global Positioning System Fix Data (GGA)

Used

Sintax

$GPGGA, <1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,M, <10>,M, <11>,<12>,*hh<CR><LF>

<1>

UTC time of position fix, hhmmss.s format

<2>

Latitude, ddmm.mmmmm (leading zeros will be transmitted)

<3>

Latitude hemisphere, N or S

<4>

Longitude, dddmm.mmmmm (leading zeros will be transmitted)

<5>

Longitude hemisphere, E o W

<6>

GPS quality indication, 0 = fix not available, 1 = Non-differential

GPS fix available, 2 = Differential GPS (WAAS) fix available, 6 =

Estimated

<7>

Number of satellites in use, 00 to 12 (leading zeros will be

transmitted)

<8>

Horizontal dilution of precision, 0.5 to 99.9

<9>

Antenna height above/below mean sea level, -9999.9 to 99999.9

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VIA Technologies EPIA SN-Series Specifications Page 90

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