topic MC68HC908JB - Problems with Input and Output in 8-bit Microcontrollers

MC68HC908JB - Problems with Input and Output

tiagodalmaso — Sat, 07 Jun 2008 00:39:50 GMT

Hi! I'm new at this forum and I hope I can get some help here.

I'm trying to use Port A for input and Output, configurable at realtime. It works if all the pins are outputs or inputs, but when I have both, the outputs don't work. I'm using the inputs as interrupts with KBI. The inputs work correctly but when I try to change an output pin it doesn't work.

Can anybody help me please? thank you!

Re: MC68HC908JB - Problems with Input and Output

donw — Sat, 07 Jun 2008 03:31:45 GMT

I have not used the KBI module, but I think I read taht if a KBI interrupt was enabled on a Port A pin,

then it over-rides the output enable bit. So you will have to disable the KBI bit for the port pin before

making it an output pin.

Check the data sheet....

Re: MC68HC908JB - Problems with Input and Output

UK_CF_FAE — Tue, 10 Jun 2008 00:25:59 GMT

Hi,

Don is correct, the use of the KBI overrides the data direction register on the port.

You want to see the note at the end of chapter 14.5.

To use the part in the way that you describe means that you need to disable the KBI function on that pin with KBIEx = 0, then set the DDR for the pin to output PTADDx = 1.

Now the pin behaves as output.

To go back to KBI, remember so set the GPIO as an input (PTADDx = 0), and re-enable KBIEx = 1.

Mark