CCurrentLimit.h

#pragma once

//#include <avr/io.h>
#include "CMcp4242.h"

// Here are some design notes for the MCP4242 current limiting
//  with the LMD18245 devices

// LMD18245 3A, 55V DMOS Full-Bridge Motor Driver:
// The LMD18245 device is rated for a maximum of 3 amps.
// Current limiting is set by a resistance between CS_OUT and GND.
// The resistance is made up of a 6.2K resistor in series with
//  a 50K rheostat in the MCP4242 device.  There are two LMD18245's,
//  and two current limiting reistor paths, so both rheostats must
//  be updated at the same time.
// Formula is 5V x 15/16 / (.00025 x R) = Amps
//  or Amps = 18750 / R  where R = 6.2K + rheostat setting

// MCP4242 Dual 50K 129-step Non-volatile Rheostat
// Each step of the rheostat is 50K/128 = 390.625 + 70 = 460.625 ohms
// Combined with the series 6.2K resistor yields total resistance of:
// 0 - 6.27K  127 - 56.19K
// 1 - 6.66K  128 - 56.60K
// 2 - 7.05K  129 - 56.60K

//  0   0   6.27K  2.99A      6  36  20.33K  0.92A
//  1   6   8.61K  2.18A      7  42  22.68K  0.82A
//  2  12  10.95K  1.70A      8  48  25.02K
//  3  18  13.30K  1.41A      9  54  27.36K
//  4  24  15.65K  1.20A     10  60  29.71K  0.63A
//  5  30  17.99K  1.04A

//  STEPS - Each step represents roughly 0.25A change
//  0   0   3.00A       4   8  2.00A    8  32   1.00A
//  1   2   2.66A   5  11  1.77A    9  48   0.75A
//  2   3   2.51A   6  16  1.50A   10  80   0.50A
//  3   5   2.28A   7  22  1.26A

// Forth Word(s)
void readCurrentLimit(void);    // -- setting or error (-1)
void writeCurrentLimit(void);   // setting --

const char settings[] = {80, 48, 32, 22, 16, 11, 8, 5, 3, 2, 0};  // Low to high current

//---------------------------------------------------------------------------- //-------------------------------------------------------------------------
class CCurrentLimit : CMcp4242
{
public:
        static void init(void)
        {
                CMcp4242::init();       // Call base class init()
        }

        static int read(void)
        {
                int wiperValue;

                wiperValue = CMcp4242::read(wiper0nv);
                for (unsigned int i = 0; i < sizeof(settings); i++)
                {
                        if (wiperValue == settings[i])
                        {
                                if (wiperValue != CMcp4242::read(wiper0))
                                        break;
                                if (wiperValue != CMcp4242::read(wiper1))
                                        break;
                                if (wiperValue != CMcp4242::read(wiper0nv))
                                        break;                  // Go to error condition
                                if (wiperValue != CMcp4242::read(wiper1nv))
                                        break;                  // Go to error condition
                                return i;                       // All 4 pot regs match
                        }
                }
                // Conversion didn't work or wipers don't match
                return -1;                                      // Return error
        }

        static void write(int setting)
        {
                // Check setting for invalid array index
                if (setting < 0 || setting >= (int)sizeof(settings))
                        return;
                if (read() == setting)          // Compare to current setting
                        return;                                 // Rheostats are alread set

                CMcp4242::write(wiper0,   settings[setting]);
                CMcp4242::write(wiper1,   settings[setting]);
                CMcp4242::write(wiper0nv, settings[setting]);
                // Wait for EEWA (EEPROM Write Active) to be inactive
                while (CMcp4242::read(status) & _BV(EEWA));             
                CMcp4242::write(wiper1nv, settings[setting]);
        }
};