' ==============================================================================
' MicroMag3 Magnetic Sensor Control Program
' Translated to MMBasic for Micromite / Maximite / PicoMite
' Based on Silicon Chip June 2024 (Jim Rowe) and September 2024 updates
' ==============================================================================

Option Explicit

' Define Pin Numbers (Adjust these to match your hardware layout)
Const pinSSNOT  = 1    ' Slave Select / Chip Select (Output)
Const pinRESET  = 2    ' Reset Line (Output)
Const pinDRDY   = 3    ' Data Ready Line (Input)
' Note: Hardware SPI pins (SDI, SDO, SCK) are automatically managed by SPI OPEN.

' Global tracking variables
Dim x_val, y_val, z_val
Dim heading_deg
Dim PI : PI = 4 * Atn(1)

' Initialise I/O Pins
SetPin pinSSNOT, DOUT : Pin(pinSSNOT) = 1 ' Set High (Idle)
SetPin pinRESET, DOUT : Pin(pinRESET) = 0
SetPin pinDRDY, DIN

' Initialise Hardware SPI channel
' Configures SPI Mode 0, Master, 8-bit data, and a safe clock speed (e.g., 100kHz)
SPI Open 100000, 0, 8

Print "MicroMag3 MMBasic Controller Initialised."
Print "-------------------------------------------"

' Main Executive Loop
Do
 x_val = ReadAxis(1) ' Read X-Axis (Command offset 1)
 y_val = ReadAxis(2) ' Read Y-Axis (Command offset 2)
 z_val = ReadAxis(3) ' Read Z-Axis (Command offset 3)
 
 heading_deg = GetHeading(x_val, y_val)
 
 Print "X: "; x_val; " | Y: "; y_val; " | Z: "; z_val; " | Heading: "; heading_deg; " deg"
 
 Pause 2000 ' Update rate (2 seconds)
Loop

' ==============================================================================
' FUNCTION: ReadAxis
' Pulses the MicroMag3, sends the axis command, and extracts 16-bit signed data
' ==============================================================================
Function ReadAxis(axisNum)
 Local cmdByte, highByte, lowByte, rawWord
 
 ' Formulate the command byte based on the desired axis:
 ' Core measurement control configuration: division ratio /2048 (Bits: 01100)
 ' End bits map: X=01 (1), Y=10 (2), Z=11 (3)
 If axisNum = 1 Then
   cmdByte = &B00110001 ' X Axis
 ElseIf axisNum = 2 Then
   cmdByte = &B00110010 ' Y Axis
 Else
   cmdByte = &B00110011 ' Z Axis
 EndIf
 
 ' 1. Cycle Reset to begin measurement sequence
 Pin(pinRESET) = 1 : Pause 2 : Pin(pinRESET) = 0 : Pause 2
 
 ' 2. Select the sensor chip
 Pin(pinSSNOT) = 0 : Pause 2
 
 ' 3. Transmit the command byte via SPI
 SPI Write 1, cmdByte
 
 ' 4. Wait for the Data Ready line to clear/assert or fall back on a safe timeout
 ' Alternatively, if bypassing IO6 as per Silicon Chip, use a hard delay (e.g., Pause 15)
 Local timeout = 0
 While Pin(pinDRDY) = 0 And timeout < 500
   timeout = timeout + 1
   Pause 1
 Wend
 
 ' 5. Retrieve 16 bits of measurement data (2 Bytes)
 highByte = SPI(0)
 lowByte = SPI(0)
 
 ' Deselect the sensor
 Pin(pinSSNOT) = 1
 
 ' Combine bytes into a raw 16-bit integer
 rawWord = (highByte * 256) + lowByte
 
 ' Handle 16-bit two's complement sign conversion
 If rawWord >= 32768 Then
   ReadAxis = rawWord - 65536
 Else
   ReadAxis = rawWord
 EndIf
End Function

' ==============================================================================
' FUNCTION: GetHeading
' Implements a manual 4-quadrant arctan safely using the standard MMBasic ATN()
' ==============================================================================
Function GetHeading(x, y)
 Local angle
 
 ' Trap zero denominators cleanly to avoid division-by-zero math errors
 If x = 0 Then
   If y < 0 Then angle = PI / 2
   If y >= 0 Then angle = 3 * PI / 2
 Else
   ' Basic single-variable arctan
   angle = Atn(y / x)
   
   ' Quadrant correction logic matching the module's magnetic framework
   If x < 0 Then
     angle = PI - angle
   ElseIf x > 0 And y < 0 Then
     angle = -angle
   ElseIf x > 0 And y > 0 Then
     angle = (2 * PI) - angle
   EndIf
 EndIf
 
 ' Convert Radians to Degrees and normalise
 Local deg = angle * (180 / PI)
 If deg < 0 Then deg = deg + 360
 
 GetHeading = Int(degMod(deg))
End Function

' Helper to tightly clamp degrees inside a 0-359 compass bounds
Function degMod(d)
 Dim outD = d
 Do While outD >= 360 : outD = outD - 360 : Loop
 Do While outD < 0    : outD = outD + 360 : Loop
 degMod = outD
End Function
Use code with caution.

Essential Conversion Notes

1. SPI Implementation: Rather than bit-banging the individual pins, the translation implements MMBasic's native hardware SPI OPEN and SPI Write / SPI() stream functions. This reflects the design principles highlighted in the original Silicon Chip article.
2. Quadrant Math (ATN vs ATAN2): Because standard MMBasic does not natively expose a two-argument ATAN2 function, the GetHeading routine features safety boundaries for X = 0 along with explicit block filters to accurately isolate the four vector quadrants.
3. Data Handling: The code transforms raw High/Low incoming bytes back into standard signed variables using 16-bit two's complement logic explicitly parsed for standard BASIC limitations.
To tailor this exactly to your hardware setup, could you let me know:
• Which specific hardware platform are you using to run MMBasic (e.g., a custom Micromite, a Maximite, or a PicoMite)?
• Do you need to adjust the default SPI channel assignments or pin numbers inside the code to match how your module is wired?
Try without personalization
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