topic Re: Some help with C code!!! in 8-bit Microcontrollers

Some help with C code!!!

damitsi — Mon, 22 Jan 2007 20:59:12 GMT

Does anybody knows a C code to do the communication between MC908GP32 and the sensor SHT11?
At Sensirion's site it has a sample code for 80c51 family microcontroller.

Thanks

Re: Some help with C code!!!

UcTechnoGeek — Tue, 23 Jan 2007 00:15:09 GMT

What kind of interface is it?

Since the GP32 was one of the first 908 devices released, I would take a look at the 908AP32. It's a similar device at a lower cost.

Better yet, take a look at the 9S08GT32A. Faster, lower power and has the built in BDM (much better for debugging). Best of all, it even cost less.

Just my two cents.

uCTechnoGeek

Re: Some help with C code!!!

alex_spotw — Tue, 23 Jan 2007 01:38:23 GMT

Hi:

If the sample code is in C, you should not have big trouble using it with the HCs08 compiler. Could you post that sample code?

Regards,

Alex R.

Re: Some help with C code!!!

peg — Tue, 23 Jan 2007 05:18:10 GMT

Hi damitsi,

I am sure we have been here before but I can't find it. Maybe it was a slightly different part?

Maybe someone else remembers?

Regards

Peg

Found the one I was thinking of, not sure if its relevant:

http://forums.freescale.com/freescale/board/message?board.id=8BITCOMM&message.id=317

Message Edited by peg on 2007-01-2307:22 AM

Re: Some help with C code!!!

bigmac — Tue, 23 Jan 2007 14:59:50 GMT

Hello,

The previous thread quoted by Peg is relevant to all devices in the family, including the SHT11. The sample C code on the Sensiron website should readily adapt to the MC9(S)08 series, since it appears to simply bit-bang the I/O pins.

You would need to define the DATA and SCK signals against the I/O you are using. Note that, for the DATA signal, you would actually be controlling the associated DDR bit, as discussed in the earlier thread. With this arrangement, the send data would be inverted, but the receive data would not - probably not applicable to 80C51 devices with open drain I/O configuration.

For example, if you were to use PTA0 for data, and PTA1 for clock -

#define DATA DDRA_DDRA0

#define SCK PTA_PTA1

Also note the previous comments with respect to floating point calculations done by the sample code.

Regards,

Mac

Message Edited by bigmac on 2007-01-2305:05 PM

Re: Some help with C code!!!

damitsi — Wed, 24 Jan 2007 05:17:46 GMT

Hi alex_spotw, for the sample code go to

http://www.sensirion.com/en/02_sensors/03_humidity/00_humidity_temperature_sensor/02_humidity_sensor_sht11.htm

and download the (Sample Code humidity sensor SHTxx .pdf )

Thank you for your interest

Regards,

Jim

Re: Some help with C code!!!

damitsi — Wed, 24 Jan 2007 05:19:40 GMT

Hi peg, first of all i would like to thank you for your help about the

communication problem that i had. Second thanks again for your link in

this forum. Now I will work on it and we will see.

Regards,

Jim

Re: Some help with C code!!!

bigmac — Wed, 24 Jan 2007 09:09:41 GMT

Hello,

As previously noted, the sample code from the Sensiron website uses floating point calculations for determining temperature, RH and dew point from the raw sensor data. The use of floating point may exceed the resources of many low end MCU devices, and should be avoided, if possible. It does seem to be feasible to use integer calculations for temperature and humidity, but not for dew point (at least not for simple coding).

The attached code would replace the calc_sth11() function of the sample code, and would provide temperature resolution of 0.1C, and humidity resolution of 0.1%RH, using short variables instead of float. This code should be much less expensive of MCU resources, assuming dew point calculation is not required.

Regards,

Mac