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I'm trying to read data from a Morningstar Sunsaver MPPT that outputs modbus in Float16, is there anyone that has done this with the modbuusmaster command?  

There is an example program on our website for the Morningstar Sunsaver MPPT using a CR1000X. It can be found here:

https://s.campbellsci.com/documents/us/miscellaneous/CR1000X-38898.dld

unfortunately, I made a mistake.  It is a TriStar MPPT, and they changed all of their output types to float16.  The example provided does work with my sunsavers for sure but no this new controller.  :(

Thanks you for the reply though!

Curt

Here's a (clunky) subroutine I whipped up to convert an Integer16 into a float16. Basically, we're just reading 2 bytes in a modbus register, converting that signed integer16 to binary, and then converting back to a float 16.

Example: Reading the battery voltage register we get back 21226

Subroutine:

Public Result, MPPTCharger, battvolts As Long, value As Float

'========FLOAT 16===========
Sub f$float16 (returnValue, int16 As Long)
  Dim binary As String, exponent As Long, i As Long, temp As Long, mantissa As Float
  binary=FormatLong (int16,"%b")
  '##EXPONENT##
  exponent = -15
  For i = 1 To 5
    temp = Mid(binary,6-i,1)
    exponent += temp*2^(i-1)
  Next i
  exponent = 2^exponent
  '##MANTISSA'
  mantissa = 0
  For i = 6 To 15
    temp = Mid(binary,21-i,1)
    mantissa += temp*2^(i-6)
  Next i
  mantissa = 1+ mantissa/1024
  If int16 < 0 Then
    mantissa = mantissa*-1
  End If
  returnValue = exponent*mantissa
EndSub

SlowSequence
  Scan (15,Sec,0,0)
    TCPOpen ("127.0.0.1",502,1,500,MPPTCharger,1)
    ModbusMaster (Result, MPPTCharger,9600,1,3,battvolts,25,1,3,200,1)
    Call f$float16(value,battvolts)
  NextScan

This returns the expected value of 55.3125. Hopefully a MoveBytes wizard can come around and do something slicker, but this is my solution until ModbusMaster can handle half-precision floats.

Here is a program developed for the Tristar by someone at CSI that we've used in the past: 

Public result
Public modin(82) As Long

Public N_sys_V

Public Charge_Current, Battery_Terminal_Voltage, Array_Current, Array_Voltage
Public Load_Voltage, Load_Current, Battery_Current
Public HeatSink_Temperature, Battery_Temperature
Public Charger_Output_Power, Array_Vmp,Array_Pmax,Array_Voc

DataTable(Power,true,-1)
DataInterval(0,30,sec,10)
Sample (1,Charge_Current,FP2)
Sample (1,Battery_Terminal_Voltage,FP2)
Sample (1,Battery_Current,FP2)
Sample (1,Load_Current,FP2)
Sample (1,HeatSink_Temperature,FP2)
Sample (1,Battery_Temperature,FP2)
Sample (1,Array_Vmp,FP2)
Sample (1,Array_Voc,FP2)
Sample (1,Array_Pmax,FP2)
Sample (1,Charger_Output_Power,FP2)
EndTable

Function LongToFloat16(SourceLong As Long) As Float   

'Takes a Float16 stored in the lower 2 bytes of a Long, and converts to a Float

Dim SignBit As Long
Dim Exponent As Long
Dim Fraction As Long
Dim tempLong As Long
Dim result As Float 'The Float16 moved into a single precision 32 bit float

Erase(tempLong)
Erase(result)

SignBit = (SourceLong >> 15) AND 1
Exponent = ((SourceLong >> 10) AND 31) -15 + 127 'Float16 has a bias of 15, Float32 has a bias of 127

If Exponent = 143 Then Exponent = 255 'NAN catch
If Exponent = 112 Then Exponent = 0 'Zero catch
Fraction = SourceLong AND 1023

tempLong = (Exponent << 23) OR (Fraction << 13 )
MoveBytes (result,0,tempLong,0,4)
If SignBit Then result = result * -1 'Since long are signed, I can't just OR the sign bit

Return result
EndFunction

BeginProg  SerialOpen (ComRS232,9600,7,0,50)

Scan (5,Sec,0,0)

'Code to measure Tristar charge controller
ModbusMaster (result,ComRS232,9600,1,3,modin(),1,82,3,100,3)

N_sys_V=LongToFloat16((modin(2)))
Charge_Current = LongToFloat16((modin(17)))
Battery_Terminal_Voltage = LongToFloat16((modin(19)))
Array_Current = LongToFloat16((modin(18)))
Array_Voltage = LongToFloat16((modin(20)))
'Battery_Sense_Voltage = LongToFloat16((modin(24)))
Load_Voltage = LongToFloat16((modin(21)))
Battery_Current = LongToFloat16((modin(22)))
Load_Current = LongToFloat16((modin(23)))
HeatSink_Temperature =LongToFloat16((modin(27)))
Battery_Temperature = LongToFloat16((modin(28)))
Charger_Output_Power = LongToFloat16((modin(61)))
Array_Vmp = LongToFloat16((modin(62)))
Array_Pmax = LongToFloat16((modin(63)))
Array_Voc = LongToFloat16((modin(64)))

CallTable power
NextScan

EndProg

Wow! Thanks everyone!  I can't wait to give it a try!

Curt