Internal Temperature sensor of LM4F232

Karthi Prime

Hi,

Consider this code snippet from Stellarisware/Examples/ADC/temperature_sensor.c:

ulTemp_ValueC = ((1475 * 1023) - (2250 * ulADC0_Value[0])) / 10230;

The value of ulADC0_VAlue[0] is 1750 (otained through UART printing); When we calculate the ulTemp_Value using this 1750, manually, we get the value -237 Celsius. But the UART printed value of ulTemp_ValueC is 419604 Celsius.

Now consider the execution of the following snippet:

ulTemp_ValueC = ((1475 * 1023) - (2250 *1750)) / 10230;

Now the Expected value is -237, and it is printed.

In either case, I havent got the actual temperature, which must be around 30 Celsius.

over 11 years ago

0 Markel Robregado over 11 years ago

Guru 86195 points

Hi Karthi,

I copied and pasted that code snippet to the hello project of my EK-LM3S6965, and works just fine. Printed out this below at Tera Term. That's the internal temperature of the chip. Expect the temp to be higher than 30 Celsius.

"Temperature = 43*C or 109*F"

-kel

0 Karthi Prime over 11 years ago in reply to Markel Robregado

Intellectual 325 points

Hi Mikel,

The code I used is: (from stellarisware/examples/peripherals/adc/temperature_sensor.c)

//*****************************************************************************

// temperature_sensor.c - Example demonstrating the internal ADC temperature

// sensor.

// Software License Agreement

// Texas Instruments (TI) is supplying this software for use solely and

// exclusively on TI's microcontroller products. The software is owned by

// TI and/or its suppliers, and is protected under applicable copyright

// laws. You may not combine this software with "viral" open-source

// software in order to form a larger program.

// THIS SOFTWARE IS PROVIDED "AS IS" AND WITH ALL FAULTS.

// NO WARRANTIES, WHETHER EXPRESS, IMPLIED OR STATUTORY, INCLUDING, BUT

// NOT LIMITED TO, IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

// A PARTICULAR PURPOSE APPLY TO THIS SOFTWARE. TI SHALL NOT, UNDER ANY

// CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL, OR CONSEQUENTIAL

// DAMAGES, FOR ANY REASON WHATSOEVER.

// This is part of revision 9453 of the Stellaris Firmware Development Package.

//*****************************************************************************

#include "inc/hw_memmap.h"

#include "inc/hw_types.h"

#include "driverlib/adc.h"

#include "driverlib/gpio.h"

#include "driverlib/sysctl.h"

#include "utils/uartstdio.h"

//*****************************************************************************

//! \addtogroup adc_examples_list

//! <h1>ADC Temperature Sensor (temperature_sensor)</h1>

//!

//! This example shows how to setup ADC0 to read the internal temperature

//! sensor.

//!

//! NOTE: The internal temperature sensor is not calibrated. This example

//! just takes the raw temperature sensor sample and converts it using the

//! equation found in the LM3S9B96 datasheet.

//!

//! This example uses the following peripherals and I/O signals. You must

//! review these and change as needed for your own board:

//! - ADC0 peripheral

//!

//! The following UART signals are configured only for displaying console

//! messages for this example. These are not required for operation of the

//! ADC.

//! - UART0 peripheral

//! - GPIO Port A peripheral (for UART0 pins)

//! - UART0RX - PA0

//! - UART0TX - PA1

//!

//! This example uses the following interrupt handlers. To use this example

//! in your own application you must add these interrupt handlers to your

//! vector table.

//! - None.

//*****************************************************************************

// This function sets up UART0 to be used for a console to display information

// as the example is running.

//*****************************************************************************

void

InitConsole(void)

{

// Enable GPIO port A which is used for UART0 pins.

// TODO: change this to whichever GPIO port you are using.

SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);

// Configure the pin muxing for UART0 functions on port A0 and A1.

// This step is not necessary if your part does not support pin muxing.

// TODO: change this to select the port/pin you are using.

GPIOPinConfigure(GPIO_PA0_U0RX);

GPIOPinConfigure(GPIO_PA1_U0TX);

// Select the alternate (UART) function for these pins.

// TODO: change this to select the port/pin you are using.

GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);

// Initialize the UART for console I/O.

UARTStdioInit(0);

}

//*****************************************************************************

// Configure ADC0 for the temperature sensor input with a single sample. Once

// the sample is done, an interrupt flag will be set, and the data will be

// read then displayed on the console via UART0.

//*****************************************************************************

int

main(void)

{

// This array is used for storing the data read from the ADC FIFO. It

// must be as large as the FIFO for the sequencer in use. This example

// uses sequence 3 which has a FIFO depth of 1. If another sequence

// was used with a deeper FIFO, then the array size must be changed.

unsigned long ulADC0_Value[1];

// These variables are used to store the temperature conversions for

// Celsius and Fahrenheit.

unsigned long ulTemp_ValueC;

unsigned long ulTemp_ValueF;

// Set the clocking to run at 20 MHz (200 MHz / 10) using the PLL. When

// using the ADC, you must either use the PLL or supply a 16 MHz clock

// source.

// TODO: The SYSCTL_XTAL_ value must be changed to match the value of the

// crystal on your board.

SysCtlClockSet(SYSCTL_SYSDIV_10 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN |

SYSCTL_XTAL_16MHZ);

// Set up the serial console to use for displaying messages. This is just

// for this example program and is not needed for ADC operation.

InitConsole();

// Display the setup on the console.

UARTprintf("ADC ->\n");

UARTprintf(" Type: Internal Temperature Sensor\n");

UARTprintf(" Samples: One\n");

UARTprintf(" Update Rate: 250ms\n");

UARTprintf(" Input Pin: Internal temperature sensor\n\n");

// The ADC0 peripheral must be enabled for use.

SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);

// Enable sample sequence 3 with a processor signal trigger. Sequence 3

// will do a single sample when the processor sends a singal to start the

// conversion. Each ADC module has 4 programmable sequences, sequence 0

// to sequence 3. This example is arbitrarily using sequence 3.

ADCSequenceConfigure(ADC0_BASE, 3, ADC_TRIGGER_PROCESSOR, 0);

// Configure step 0 on sequence 3. Sample the temperature sensor

// (ADC_CTL_TS) and configure the interrupt flag (ADC_CTL_IE) to be set

// when the sample is done. Tell the ADC logic that this is the last

// conversion on sequence 3 (ADC_CTL_END). Sequence 3 has only one

// programmable step. Sequence 1 and 2 have 4 steps, and sequence 0 has

// 8 programmable steps. Since we are only doing a single conversion using

// sequence 3 we will only configure step 0. For more information on the

// ADC sequences and steps, reference the datasheet.

ADCSequenceStepConfigure(ADC0_BASE, 3, 0, ADC_CTL_TS | ADC_CTL_IE |

ADC_CTL_END);

// Since sample sequence 3 is now configured, it must be enabled.

ADCSequenceEnable(ADC0_BASE, 3);

// Clear the interrupt status flag. This is done to make sure the

// interrupt flag is cleared before we sample.

ADCIntClear(ADC0_BASE, 3);

// Sample the temperature sensor forever. Display the value on the

// console.

while(1)

{

// Trigger the ADC conversion.

ADCProcessorTrigger(ADC0_BASE, 3);

// Wait for conversion to be completed.

while(!ADCIntStatus(ADC0_BASE, 3, false))

{

}

// Clear the ADC interrupt flag.

ADCIntClear(ADC0_BASE, 3);

// Read ADC Value.

ADCSequenceDataGet(ADC0_BASE, 3, ulADC0_Value);

// Use non-calibrated conversion provided in the data sheet. Make

// sure you divide last to avoid dropout.

ulTemp_ValueC = ((1475 * 1023) - (2250 * ulADC0_Value[0])) / 10230;

// Get fahrenheit value. Make sure you divide last to avoid dropout.

ulTemp_ValueF = ((ulTemp_ValueC * 9) + 160) / 5;

// Display the temperature value on the console.

UARTprintf("Temperature = %3d*C or %3d*F\r", ulTemp_ValueC,

ulTemp_ValueF);

// This function provides a means of generating a constant length

// delay. The function delay (in cycles) = 3 * parameter. Delay

// 250ms arbitrarily.

SysCtlDelay(SysCtlClockGet() / 12);

}

I ran this code on LM4F232 kit and got the value Temperature = 419602*C or 755322*F.

Where could be the mistake?

0 Markel Robregado over 11 years ago in reply to Karthi Prime

Guru 86195 points

Hi,

I used the same code. The only difference is my uc is Fury Class, and I commented out the GPIOPinConfigure(). I am out of ideas, why you are getting those values. If I would guess, try lowering the optimization of your compiler to -O0, and see if you still get the same values..

-kel

0 cb1 over 11 years ago in reply to Markel Robregado

Guru 47900 points

Your problem is the 1023 value & old equation - that is for older/past M3 which had 10 bit A to D.

Newer LX4F and rebrand have graduated to 12 bits (4095/6).

From w/in my LX4F MCU manual - ADC Section: " Temperature = 147.5 - ((225 × ADC) / 4095)"

Running these numbers (w/your 1750 value) yields Temp = 147.5 - 96.2 = 51.3° C (should be good for G'ovt Work...)

Caution: for you/others - many code examples were developed for MCUs current - at that time! May not be fully appropriate when copied and used - w/out proper "adapting" into agreement w/ latest/greatest MCUs.

Your failed UART print value appears to be another matter - and is outside of the subject/title of this posting. (make a 2nd thread (new posting) for that - if that UART print value continues to defy logic.) Forum owner advises against multiple subjects w/in one thread - this confounds future "searches/answers..."

Perhaps you'll "consider" Green Verify Answer - always gratefully accepted - merci...

0 Karthi Prime over 11 years ago in reply to cb1

Intellectual 325 points

Hi cb1,

The LM4F232H5QD datasheet says the formula as: TEMP = 147.5 - ((75 * (VREFP - VREFN) × ADCCODE) / 4096);

How did you quote the formula as TEMP = 147.5 - ((225 * (VREFP - VREFN) × ADCCODE) / 4096) in your reply??

Thanks!

0 cb1 over 11 years ago in reply to Karthi Prime

Guru 47900 points

Thank you - appreciated. Glad that my writing encouraged you to check your MCU datasheet.

As stated (my answering post) formula I presented was direct extract from our LX4F - 64 pin MCU. This smaller pin-count device (at least ours) does not include the VREFP nor VREFN pins - likely explaining formula's difference. In fact - replacing those VREFs w/ 3.0 (3.0V - 0V) yields 75 * 3 = 225. Q.E.D. (perhaps warrants 2nd green)

You were sufficiently resourceful to find and employ that code example. Recall that LM3S was vendor's sole issue for ~first five years - thus many examples so targeted. Newer LX4F (and rebrand) overlap many - but not all - capabilities & functions - thus you must be "on guard" for critical differences when importing code not specifically targeting your MCU...

0 loehr_andreas over 10 years ago in reply to cb1

Prodigy 10 points

Hello.

Im sitting here on a similar problem. I try to use the example temperature_sensor.c to get the temperutre from the bord and to send it via usb to the computer. can someone help me to integrate the c-code in (for example) the example usb_dev_serial.uproj

Im using the EKK LM4F232.

would be great.

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Internal Temperature sensor of LM4F232