Overview

At this point we've got all the tools we need to start mapping the station data into the MODBUS register space. We'll also need some of the observations later for the derived calculations so we'll define a structure to collect them.

struct vp2_conditions {
    double temp;    // F
    double bar;     // inHg
    double hum;     // percent
    double wind;    // mph
    double rad;     // W/m^2
    double dew;     // F
    double den;     // kg/m^3
};			
			

I've configured the console to use United States customary units rather than metric only because they're more familiar. If you opt for metric, remember to adjust your constants.

Formatting Bit, Integer and Real Values

Using the protocol reference and the conversion tools the last section we just map the observations one by one.

void vp2_update(USHORT *pucRegBuffer) {

    unsigned char *ptr = (unsigned char *) usb_buffer();
    int i, modptr = 0;
    static struct vp2_conditions cond;
    
    /* 40001 int(1)   Barometer Trend (enumerated) */
    pucRegBuffer[modptr++] = SBTOB(3);

    /* 40002 float(2) Barometer (in Hg) */
    modptr += vp2_pack_float(cond.bar = (DBTOW(7) / 1000.0), &pucRegBuffer[modptr]);

    /* 40004 float(2) Inside Temperature (F) */
    modptr += vp2_pack_float(DBTOW(9) / 10.0, &pucRegBuffer[modptr]);
	
    ....
	
}

When the code is compiled, we should be able to retrieve values such as the outside temperature from the application using a utility like modpoll.

$ modpoll -m tcp -r 40008 -t 4:float -f 127.0.0.1

Observation Register Map

This station doesn't use any additional sensors but I've allocated space for them anyway. The complete observation register map looks like this:

Register	Name	Type	Units	Notes
40001	Barometer Trend	int	enumerated
40002	Barometer	float	in Hg
40004	Inside Temperature	float	F
40006	Inside Humidity	float	%
40008	Outside Temperature	float	F
40010	Wind Speed	float	mph
40012	10 Minute Average Wind Speed	float	mph
40014	Wind Direction	float	degrees	0 indicates no value, 1..360
40016	Extera Temperature 1	float	F	Optional
40018	Extera Temperature 2	float	F
40020	Extera Temperature 3	float	F
40022	Extera Temperature 4	float	F
40024	Extera Temperature 5	float	F
40026	Extera Temperature 6	float	F
40028	Extera Temperature 7	float	F
40030	Soil Temperature 1	float	F	Optional
40032	Soil Temperature 2	float	F
40034	Soil Temperature 3	float	F
40036	Soil Temperature 4	float	F
40038	Leaf Temperature 1	float	F	Optional
40040	Leaf Temperature 2	float	F
40042	Leaf Temperature 3	float	F
40044	Leaf Temperature 4	float	F
40046	Outside Humidity	float	%
40048	Extra Humidity 1	float	%	Optional
40050	Extra Humidity 2	float	%
40052	Extra Humidity 3	float	%
40054	Extra Humidity 4	float	%
40056	Extra Humidity 5	float	%
40058	Extra Humidity 6	float	%
40060	Extra Humidity 7	float	%
40062	Rain Rate	float	in/hr
40064	UV Index	float
40066	Solar Radiation	float	W/m^2
40068	Storm Rain	float	in
40070	Start Date of Current Storm	int		Year
40071				Month
40072				Day
40073	Day Rain	float	in
40075	Month Rain	float	in
40077	Year Rain	float	in
40079	Day ET	float	in
40081	Month ET	float	in
40083	Year ET	float	in
40085	Soil Moisture 1	float	centibar	Optional
40087	Soil Moisture 2	float	centibar
40089	Soil Moisture 3	float	centibar
40091	Soil Moisture 4	float	centibar
40093	Leaf Wetness 1	int	enumerated	Optional, 0 .. 15 (very dry to very wet)
40094	Leaf Wetness 2	int	enumerated
40095	Leaf Wetness 3	int	enumerated
40096	Leaf Wetness 4	int	enumerated
40097	Inside Alarms	int	bitmap
40098	Rain Alarms	int	bitmap
40099	Outside Alarms 1	int	bitmap
40100	Outside Alarms 2	int	bitmap
40101	Outside Humidity Alarms	int	bitmap
40102	Extra Temperature/Humidity Alarms 1	int	bitmap	Optional
40103	Extra Temperature/Humidity Alarms 2	int	bitmap
40104	Extra Temperature/Humidity Alarms 3	int	bitmap
40105	Extra Temperature/Humidity Alarms 4	int	bitmap
40106	Extra Temperature/Humidity Alarms 5	int	bitmap
40107	Extra Temperature/Humidity Alarms 6	int	bitmap
40108	Extra Temperature/Humidity Alarms 7	int	bitmap
40109	Soil and Leaf Alarms 1	int	bitmap	Optional
40110	Soil and Leaf Alarms 2	int	bitmap
40111	Soil and Leaf Alarms 3	int	bitmap
40112	Soil and Leaf Alarms 4	int	bitmap
40113	Transmitter Battery Status	int	enumerated	0 is ok
40114	Console Battery Voltage	float	V
40116	Forecast Icons	int	bitmap
40117	Forecast Rule	int	enumerated
40118	Console Sunrise	int	hour	0..23
40119		int	minute	0..59
40120	Console Sunset	int	hour	0..23
40121		int	minute	0..59