afterburner/aftb_mcp4131.h
ole00 3ee0147d88 sketch: improved calibration, mcp4151 uses full tap scale
This change stores the digi pot indices in the scale 1-255
(previously 1 -128) so the stored values for calibration
are no longer valid after this change is uploaded to Arduino.

Please re-run the full calibration on your Afterburner!
2024-03-17 21:15:05 +00:00

167 lines
4.2 KiB
C

//MCP4151 digital pot (bitbanged control) for Afterburner GAL project.
// * compatible with MCP4131 (resolution of the wiper is divided by 2)
// * the storage for tap indices is 8bit wide, therefore we must not use index 256.
// 2024-02-02 Minor change
#ifndef __AFTB_MCP4131_H__
#define __AFTB_MCP4131_H__
//set default pins
#ifndef POT_CS
#define POT_CS A3
#endif
#ifndef POT_CLK
#define POT_CLK A4
#endif
#ifndef POT_DAT
#define POT_DAT A5
#endif
#ifndef POT_DEFAULT_VALUE
#define POT_DEFAULT_VALUE 0x40
#endif
#ifndef POT_WIPER_ENABLED
#define POT_WIPER_ENABLED 0
#endif
#define ADDR_WIPER 0
#define ADDR_WIPER0 0
#define ADDR_WIPER1 1
#define ADDR_TCON 4
#define ADDR_STAT 5
#define ADDR_INCREMENT 100
#define CMD_READ (0b11 << 10)
#define CMD_INCREMENT (0b01 << 2)
#define mcp4131_disableWiper() mcp4131_write(ADDR_TCON, 0b111111101)
#define mcp4131_enableWiper() mcp4131_write(ADDR_TCON, 0b111111111)
#define mcp4131_read(A) mcp4131_reg((A),0,1)
#define mcp4131_write(A,V) mcp4131_reg((A),(V),0)
static uint8_t mcp4131_detected;
// read or write the mcp4131 register
static uint16_t mcp4131_reg(uint8_t address, uint16_t value, uint8_t read_reg) {
int8_t i = 15; //16 bit command
uint16_t r = address;
r <<= 12;
if (mcp4131_detected && address == ADDR_WIPER) {
value >>= 1; //divide the wiper value by 2
value++; // ensure we use the last tap (index 128)
}
if (address == ADDR_INCREMENT) {
r = CMD_INCREMENT;
i = 7; // 8 bit command
} else
if (read_reg) {
r |= CMD_READ;
} else {
r |= value & 0x1FF; // clamp value to 9 bits
}
//setup Clock and and Data (SPI mode 0,0)
digitalWrite(POT_CLK, 0);
digitalWrite(POT_DAT, 0);
delayMicroseconds(50);
//activate IC
digitalWrite(POT_CS, 0);
while (i >= 0) {
//write address and command (bits 15 to 10)
if ((!read_reg) || i > 9) {
uint16_t mask = (1 << i);
digitalWrite(POT_DAT, (r & mask) ? 1 : 0);
}
digitalWrite(POT_CLK, 1); //rise the clock
//only when reading reg
if (read_reg) {
//switch the DAT pin to Input
if (i == 10) {
pinMode(POT_DAT, INPUT);
}
//read bits 9 to 0
if (i < 10) {
r |= (digitalRead(POT_DAT) << i); //read after rising edge
}
}
digitalWrite(POT_CLK, 0); //fall the clock
i--;
}
if (read_reg) {
pinMode(POT_DAT, OUTPUT);
}
if (mcp4131_detected && address == ADDR_WIPER && read_reg) {
r--;
r >>= 1; //multiply the wiper value by 2
}
//disable IC
digitalWrite(POT_CS, 1);
return r & 0x1FF; //clamp value to 9 bits
}
static void mcp4131_init(void) {
pinMode(POT_CS, OUTPUT);
pinMode(POT_CLK, OUTPUT);
pinMode(POT_DAT, OUTPUT);
digitalWrite(POT_CS, 1); //unselect the POT's SPI bus
}
// initialisation and detection
// returns 1 if POT is detected, 0 otherwise
static uint8_t mcp4131_detect(void) {
uint16_t r;
mcp4131_detected = 0;
mcp4131_disableWiper();
//note checking is done while the wiper is disabled - no resistance is applied
mcp4131_write(ADDR_WIPER, 0b1010);
r = mcp4131_read(ADDR_WIPER);
if (r != 0b1010) {
return 0;
}
mcp4131_write(ADDR_WIPER, 0b101);
r = mcp4131_read(ADDR_WIPER);
if (r != 0b101) {
return 0;
}
//sanity check whether the incrementing works
mcp4131_write(ADDR_WIPER, 127);
mcp4131_write(ADDR_INCREMENT, 0);
r = mcp4131_read(ADDR_WIPER);
if (r != 128) {
return 0;
}
//detect MCP4151 by incrementing again - MCP4131 clamps the value to 128, MCP4151 increments to 129
mcp4131_write(ADDR_INCREMENT, 0);
r = mcp4131_read(ADDR_WIPER);
#if 0
Serial.print(F("MCP4151 detect: "));
Serial.println(r == 129 ? 1 : 0, DEC);
#endif
if (r == 128) {
mcp4131_detected = 1;
} else
if (r != 129) {
return 0; //error - the value should be either 128 (clamped by mcp4313) or 129 (mcp5151)
}
mcp4131_write(ADDR_WIPER, POT_DEFAULT_VALUE);
#if POT_WIPER_ENABLED
mcp4131_enableWiper();
#endif
return 1;
}
#endif