BASIC SWITCH USAGE

[sheetanshkaushi]

Hi! I am new to microcontroller programming so please be patient. the following will seem like a stupid question.

I am using DEMO9S08AW60E and using Codewarrior(Version: 5.9) with PE.

-------------Code Begins.

PTFDD = 0x00;  // to activate/intialize the port F and D

PTDDD = 0x00;

if ((PTDD_PTDD2 |= 0x02))

{

      PTFD_PTFD0 |=0x01;

}

else

{

PTFD_PTFD0 &=0x01;

}

-------------Code Ends.

link for DEMO9S08AW60E: http://cache.freescale.com/files/microcontrollers/hardware_tools/schematics/DEMO9S08AW60_SCH.pdf

According to the schematic of the board, Switch 4 is connected to PortD/Pin2. And the set of LED are connected to the PortF/Pin(0-7). I have used a pull up resistor with the help of PE. The idea is to switch on the Led when the swtich is pressed.  Logically i feel my code is fine but there doesnt seem to be any effect. I would like to know where i am going wrong and hope you will able to help.

And also it will be great if someone could tell me how to add delay in a loop for example when i am using if else loop.

THANKS in advance!

[Lundin · Accepted solution]

How to enable pull resistors in HCS08 is pretty much undocumented in the manual. What you have to do is this:

- Write to PTnPS to enable interrupts. Yes, it doesn't make sense. But it will enable the next register, PTnES.

- Write to PTnES to select interrupt edge trigger. Yes, it doesn't make sense. But it will at the same time set the pull resistor polarity: pull-up or pull-down.

- Write to PTnPE to enable the pull resistor.

- Write zero to PTnDD to set the pin as input.

---

That being said, your code has the following problems:

- You aren't using any contact de-bouncing. You need some form of simple contact de-bouncing algorithm, or your program will read random inputs from the switch.

- You are using the bitwise operators incorrectly. To check if a port input is set, you should have written PTDD_PTDD2 & 0x02, meaning "if the port AND the value 0x02 gives me 0x02 rather than 0x00 as result, then...". Similarly you are setting the output incorrectly, it should have been PTFD_PTFD0 |= 0x01; // set to pin to 1, or PTFD_PTFD0 &=~0x01; // set pin to 0.

Also, you seem to be using Freescale's default register map with non-standard bit-fields. Since that crappy register map isn't written in standard C, nobody knows what will happen when you write 0x02 to a single bit, the C standard doesn't document or specify it. I would personally stick to C instead of using Freescale non-standard features.

[sheetanshkaushi]

THANKS A LOT, DON WOOD.  That was truly the help i needed.
Just one question, SO my Logic is wrong? i should always use Masks to access the ports, right??

Also, would you explain a little more about the Last paragraph of your's; specially what do you mean by " ... I would personally stick to C instead of using Freescale non-standard features."
Thanks again!!

[Lundin]

Yes your logic is wrong, you need to study how to correctly use the bitwise operators in C.

Regarding standard C, Freescale provides a default register map which is implemented using non-standard bit fields. Your code is trying to write more than 1 bit to a single bit location in their bit-field. What happens when you do that, nobody can tell, since Freescale's register maps aren't standard.

Personally I generate my own register maps using a little parser program I've written, which goes through the MCU manual pdf and fetches every register name and bit mask from there, then generates code which is 100% conforming with the C standard.

I think it is sad that Freescale can't deliver libraries that are compliant with standard C and MISRA-C. Instead they focus on providing buggy Eclipse IDEs that nobody asked for. Apparently their new target customers are hobbyist PC programmers, rather than professional car manufacturers.

[sheetanshkaushi]

i have learned about my mistake. thank you for tat.

[donw]

The PortD needs to be initilised to output ports:   PTDDD bits should be set to 'ones'

[sheetanshkaushi]

Thank you DON Wood, i realised my mistake and corrected but the problem still remains.