Read RSC pressure sensor honeywell

[ntrungtruc2003]

Dear Sir

I use PIC16F connect to RSCDRRM020NDSE3 Honeywell SPI.
I can read EPROM register, but I don't know how to correct HEX to float.

The value returned from eprom:
address 31-------------0x42
address 32-------------0x00
address 33-------------0x00
address 34-------------0xA1

I check with https://gregstoll.dyndns.org/~gregstoll/floattohex/
the float 0x42 00 00 A1 = 32.0006

But in my function it returns a value that i don't understand.

The test function 1:

[Ttelmah]

Two separate things:

The first is that you can't change the physical value from an int32, using the cast like this. The cast takes the value represented by the int32.
The int32 value 0x42000001, is 1107296417 .
You can do either using a union, or by co-locating two variables, or by using a make32. Since you show the latter, I'll stick with this.

However then there is the problem of numeric formats.

The PIC does not use IEEE float. It uses a format specifically designed for efficiency in the chip.
Fortunately, CCS supply routines to convert IEEE floats to CCS.
These are in the library "ieeefloat.c".
If you look, the function f_IEEEtoPIC, accepts an int32 (not signed), and returns a CCS compatible float from this. So your function becomes:

[ntrungtruc2003]

Thanks sir


With Pressure minimum parameter = 0x 42 00 00 A1 this function return 32.00, it is true with IEEE float

[PCM programmer]

[ntrungtruc2003]

Thanks Sir

after remove #include<stdlib.h> from main.c , the result is true = 4.7683E-07
#include<stdint.h>

[Ttelmah]

It may well be a fault with the conversion library on this version (probably how it moves the sign bit). Back before this library existed, code to do the IEEE to PIC conversion was discussed and published here, so it'd perhaps be worth trying using a version of this code.
I did versions ages ago at:

<http://www.ccsinfo.com/forum/viewtopic.php?t=24722&highlight=ieee+ccs>

Ow. Just seen your reply while I was typing. That is very odd!..
However at least you have it working now.

[ntrungtruc2003]

Thanks Sir

Next step, I read ADC temperature from RSC sensor, but the value return is 0xFF or 0x00, Following datasheet on 3.1 https://sensing.honeywell.com/honeywell-sensing-trustability-rsc-series-data-sheet-32321348-b-en.pdf

On pin DRDY pulse = 2*Tmod (part 3.1 on datasheet), what is the value of Tmod ?

Step 1: output_low(CS_ADC); //
Step 2: spi_xfer(RSC_ADC,0x44); // initialize all register
Step 3: spi_xfer(RSC_ADC,0x06); // reset ADC
Step4: spi_xfer(RSC_ADC,0x44); // configure register number 1
Step5: spi_xfer(RSC_ADC,0x06); //set bit 1 = temperature of register 1 refer 3.5

[Ttelmah]

It's worth understanding what this module actually is.
It's a hybrid. Comprises a little circuit, with an ADC, an EEPROM, and some interconnection circuitry together with the piezo pressure transducer.
The ADC is a Texas ADS1220.
This contains the temperature sensor.

If you read this ADC data sheet, it explains DRDY.

"t(MOD) = 1 / f(MOD). Modulator frequency f(MOD) = 256 kHz (normal mode, duty-cycle mode) and 512 kHz (turbo mode), when using the
internal oscillator or an external 4.096-MHz clock."

This actually depends on the configuration bytes which must be copied from the EEPROM.

Now, you don't show us your SPI setup. Hopefully you have 'BITS=8', otherwise spi_xfer will be attempting to send 32bits each time.

Unfortunately the Honeywell sheet is appalling... DRDY, is an _output_ from the unit, which says the conversion has completed.

[ntrungtruc2003]

Thank Sir for Texas ADS1220 in this sensor.

The adc temperature read back, but i have a problem with calculate

temp[3] = 0x10
temp[2] = 0xB6
temp[1] = 0xC0
temp[0] = 0xFF

get 14 bit first _0001_0000_1011_01 = 1069*0.03125 = 33.40625 degree, it it true

but in float Temperature(void) printf("\r\nTemperature = %f", Temperature()); the value return is about 4.76E-07

[ntrungtruc2003]

case 1:

[Ttelmah]

Read the data sheet for the ADC. It tells you the maths that has to be applied to convert this value to a signed int.
The temperature is _not_ coded as a float. It is a simple integer (2's complement for -ve) count from the ADC.
You need to throw away the second pair of bytes completely, put into a signed int16, and then if bit 13 is set (-ve number), perform the ones complement (~), and add one, to give the negative value. You will then have to set bit 15 in a _signed_ int16 result.

[ntrungtruc2003]

Thanks Sir

After checked with datasheet, the calculated temperature is true. I just read the positive temperature therefore don't need to process sign bit, the full function to calculate temperature will be done later.

[Ttelmah]

Don't ignore what the data sheet is telling you.....

The temperature is _not_ stored as a float. It is an integer. You will be getting the wrong value using the IEEE float conversion on it. This is needed for the values stored in the EEPROM as floats. It is not wanted/needed for the value returned as an integer.

It is becoming repetitive to keep telling you to read the data sheet.

I charge £1500 a day to write code. If you want me to code it for you I will. Otherwise you need to stop expecting us to write this for you.

[ntrungtruc2003]

Thanks Sir

I will try to solve my problem

[ntrungtruc2003]

Hi, after read AD1220 datasheet again, I know the time conversation is tclk * 204850 = 0.8 ms with clk =256khz.

But the adc press return press[3] = 0x00, press[2]= 0x37, press[1] =0xAC press[0] =0xFF.

I don't know with the MSB data of adc pressure = 0x00, is it true or wrong ?