8-bit MicrocontrollersのトピックUnused IRQ Pin Termination - MC9S08AW32

Unused IRQ Pin Termination - MC9S08AW32

Luigi — Tue, 20 Jan 2009 23:01:20 GMT

I am using an MC9S08AW32 processor and I will not be using the IRQ function. I need to know how to terminate the unused pin. The literature is a bit confusing in that it describes that an "optional" internal pull-up or pull-down resistor can be used. It says, "when this [IRQPE] bit is set, either an internal pull-up or an internal pull-down resistor is enabled depending on the state of the IRQEDG bit." Does that mean when IRQPE = 0 there is no internal resistor selected?

I just need to know whether to pull the pin low externally or not. I guess I could just do that, but I was not sure if an internal resistor was also active. Suggestions? Thanks.

Lou

Added p/n to subject.

Message Edited by NLFSJ on 2009-01-26 07:56 AM

Re: Unused IRQ Pin Termination

Ake — Wed, 21 Jan 2009 16:43:58 GMT

Hi,

If you want to use the IRQ pin, as an IRQ, set the IRQPE bit om the IRQSC register to 1.

If you have set the IRQPE pin, you can select if you want to have falling or rising edge triggering the IRQ interrupt, by clearing setting IRQEDG bit.

The IRQPE is cleared as default, so initially the IRQ interrupt is disabled.

If you don't want to use the IRQ pin at all, I would connect a 10 kOhm pullup resistor and a 0.1 uF capacitor to the IRQ pin, and not write anything to the IRQSC register.

Did that answer your question?

Regards,

Ake

Re: Unused IRQ Pin Termination

Luigi — Fri, 23 Jan 2009 01:29:47 GMT

The second half of what you wrote did. Is your answer based on what Freescale has said about the pin, or your own best guess? I am just curious if anyone knows for sure if this pin truly floats if it is not used. I will default to pulling it high unless I hear otherwise, but I wondered if anyone else had investigated this. Thanks.

Lou