Servo - January 2008

Program 1

‘Dios NEMA Proccessor
func main()

clear
hsersetup baud,HBAUD4800,start,txon,clear

and populates the global variables shown in Table 2 when the appropriate command is received.

When a command is received, the variable NEMAcmd will be set to 1, 2, or 3, depending on the command received as shown next.

print “Mode Lat   Long      Alt    Speed  Dir”
print “—— ——- ———    ——-  ——-  ——-”

loop:
  procNEMA()
  printNEMA(9)

if NEMAcmd = 3 then ‘GGA
  if NEMAfix > 0 then
      print NEMAfix,”:”,NEMAsats,” “,{-6.0} NEMAlatmin,” “,NEMAlongmin;
      print “ “,{6.1} NEMAaltitude,” “,{4.1} NEMAspeed,” “,NEMAdir
  else
      print “No Fix “,NEMAfix,”:”,NEMAsats
  endif
endif

• 0: No command received

• 1: Non RMC or GGA command received

• 2: RMC command received

• 3: GGA command received

goto loop

endfunc

include \lib\DiosNEMA.lib

Wire the module according to the previous section and program the

appropriate program into the DiosPro using the Dios compiler. Once the GPS

module locks on to three satellites, the program will start to display the positional data shown in Figure 13.

FIGURE 13

DiosNEMA Library

The Dios Compiler has a NEMA library built in called DiosNEMA. This library processes both the GGA and RMC commands

FIGURE 14

In most cases, I don’t do any processing unless the NEMAcmd is set to a value of 3 (GGA). Once I have a valid NEMA command, I then check the NEMAfix variable to see if the module has a valid fix on at least three satellites. If it does not, then all the remaining variables are invalid.

There are a few other considerations you need to keep in mind when using the library. First, you must set up the UART using the hsersetup command shown in Program 1. In the case of the EM-406, we have set the baud rate to 4800. The UART handler built into the DiosPro is interrupt driven so data is automatically placed into a 256 byte buffer for you. It is important that you call the procNEMA() frequently, enough to keep this buffer from filling up.

The Dios NEMA library also has a command called printNEMA. This command will allow you to send the current NEMA text to the debug window. You pass a single argument to the function with the following results: