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max31855.asm

 2022/01/19
Table of Contents
AVR pAVRlib

A device driver of MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter for AVR. This code is a part of pAVRlib.

Requirement

The followings are also required if you use this program with USE_USART:

How to use

Define F_CPU (frequency of CPU) and the port settings of CK (clock), CS (chip select) and DO (data output) before you call the functions.

  • MAX_CK_DDR, MAX_CK_PORT, MAX_CK_PIN, MAX_CK

  • MAX_CS_DDR, MAX_CS_PORT, MAX_CS_PIN, MAX_CS

  • MAX_DO_DDR, MAX_DO_PORT, MAX_DO_PIN, MAX_DO

max31855-config.h will be included if you define USE_MAX31855_CONFIG.

For example:

  #ifndef __MAX31855_CONFIG_H__
  #define __MAX31855_CONFIG_H__

  #define	MAX_CK_DDR	DDRD
  #define	MAX_CK_PORT	PORTD
  #define	MAX_CK_PIN	PIND
  #define	MAX_CK		7

  #define	MAX_CS_DDR	DDRD
  #define	MAX_CS_PORT	PORTD
  #define	MAX_CS_PIN	PIND
  #define	MAX_CS		6

  #define	MAX_DO_DDR	DDRD
  #define	MAX_DO_PORT	PORTD
  #define	MAX_DO_PIN	PIND
  #define	MAX_DO		5

  #endif /* __MAX31855_CONFIG_H__ */

Subroutine

In this section "TCTemp" means a thermocouple temperature and "IntTemp" an internal (cold-junction) temperature.

void MAX31855_INIT_PORTS() (in: (none), out: (none))

initializes the ports (pins). You need define MAX_CK_DDR etc. (see above) before you call this function.

unsigned long MAX31855_READDATA() (in: (none), out: r25:r24:r23:r22)

read data from MAX31855 and returns a raw data. See the data sheet of MAX31855 for more details.

unsigned long MAX31855_FORMAT_TEMP(unsigned long rawdata) (in: r25:r24:r23:r22, out: r25:r24:r23:r22)

converts a MAX31855 raw data to 14 bit (12.2) and 12 bit (8.4) format temperatures. See also the data sheet of MAX31855.

  • r25:r24 : TCTemp

D15 D14 D13 … D0
Sign Sign MSB $2^{10}$ … LSB $2^{-2}$

  • r23:r22 : IntTemp

D15 D14 D13 D12 D11 D10 … D0
Sign Sign Sign Sign Sign MSB $2^{6}$ … LSB $2^{-4}$

unsigned long MAX31855_TCTEMP_BCD(unsigned int TCTemp) (in: r25:r24, out: r25:r24:r23:r22)

converts a TCTemp of 14 bit format to BCD. In r25:r24 will be stored the integer part of absolute value of TCTemp in BCD and in r23:r22 the fraction part of absolute value of TCTemp in BCD.

Example:

If you call this routine with r25:r24 = 0000 0001 1001 0011 (= +100.75), it will return r25:r24:r23:r22 = 0x01:0x00:0x75:0x00 (r22 is always 0x00).

unsigned long MAX31855_INTTEMP_BCD(unsigned int IntTemp) (in: r25:r24, out: r25:r24:r23:r22)

converts a IntTemp of 12 bit format to BCD. In r25:r24 will be stored the integer part of absolute value of IntTemp in BCD and in r23:r22 the fraction part of absolute value of IntTemp in BCD.

Example:

If you call this routine with r25:r24 = 0000 0110 0100 1001 (= +100.5625), it will return r25:r24:r23:r22 = 0x01:0x00:0x56:0x25.

void MAX31855_USART_TCTEMP(int TCTemp) (in: r25:r24, out: (none))

shows TCTemp via USART. This routine will be assembled only when USE_USART is defined.

Note that

  • the leading 0s are not truncated, and

  • no newline will be sent.

void MAX31855_USART_INTTEMP(int IntTemp) (in: r25:r24, out: (none))

shows IntTemp via USART. This routine will be assembled only when USE_USART is defined.

Note that

  • the leading 0s are not truncated, and

  • no newline will be sent.

Examples

../examples/max31855-test.asm

This program reads data from MAX31855 and shows the data via USART for each second.

See also: examples/README.org

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